Your last comment made me laugh...prob not appropriate but who cares..least you're honest! It sounds to me like your SD is jealous and from what you are saying I think this is normal. The baby at 10 months has moved from being a novelty to being a reality in the 4yo eyes. From what I know this is common even in full biological siblings. It sounds like your DH is doing a great job with spending time with all the kids. I think that discipling the 4yo inappropriate behaviour is definitely warranted but I also think that at this age and at this point she needs consistant reassurance (in moderation).

Perhaps you can emphasise her role as a "big sister" and give her age appropriate responsibilities that she would enjoy, can she help bath or feed? Can she tell him a story with picture books? Let her pick the babies outfit. What does she think the baby would like for dinner - pumpkin or peas? Tell her that she is a big girl and her brother needs help and her protection. Praise her when she plays nicely or "helps" him. On the flip side, at 4yo she has no concept of consequences. I strongly advise you not to leave her alone with the baby at ANYTIME! If you go to the toilet, take the baby with you, if you leave the room, even if only for a minute, take the baby with you.

Daddy is Dad's name. What else should she call him? The girl gets two 48hrs a month with her father. Baby gets 30 days with 15 of those with no other children in the home.

The baby is now mobile. Running around the house and getting into much more than what Baby has been. You really need baby safety locks on drawers and cupboards in the kitchen. Remind SD to be gentle. You'd be just as angry is there where danger in that drawer and SD just stood there and watched Baby dig in. SD had the right idea but she doesn't have the maturity to supervise a baby

I understand how you feel, my SS5 has been getting increasingly rough with BS1. He sent him flying into the floor hitting busting his head open the other night which resulted in an ER visit for some glue. A few weeks later BS1 mysteriously has his elbow yanked out of socket and it's another trip to the ER for them to fix it. Even today I let them jump on their brand new trampoline (Thanks grandma) and I caught him purposely jumping down behind BS1 to make his knees buckle and fall. He thought it was funny and luckily BS1 is a tough little nugget but it's still dangerous.

So now that you've read all that you need to understand that this is an age thing and not a "step" thing. At four and young five, they have no concept of personal space and are just now realizing that they can actually cause another child pain, joy, whatever. It's interesting to them. You say your DH parents, so does mine; he's a wonderful dad for the most part but even in nuclear homes there are times when siblings get too rough and someone gets hurt. If your DH is punishing her accordingly then the only thing left for you to do is be more vigilant when the two are together. I watch SS closely his first few days back from BMs because he takes him a while to adjust to playing with his brother that is four years younger than him versus his other brother who is only a little more than two years younger. DH likes to tell SS "be careful because accidents ARENT suppose to happen"

Apparently, you are wearing your "Resting Bitch Face" actively. Jeez, woman, a whole bunch of folk offered you perspective and suggestions and you are systematically rejecting everything. Good luck and too bad for your SD ...

Sounds like SD is jealous . You seem To be doing all you caN do . I have just noticed my SS12 has changed around my son 2 years . He was really excited about having a brother at first maybe the novelty has worn off . Now when he's over every 2nd wend he withholds toys from him ! And won't share chips or lollies etc causing my toddler to cry . It's not hard to hand over a chip !
Makes me so pissed off ! What can you do ? I am trying to speak out . I have caught him a few times and I say HEY ! Give him his car etc . I hear him cry and I know his annoying him . My SS also goes overboard with the " i luv you daddeee " spew ! In a baby voice over and over .
It's really hard but do what you have to do . i would just suggest to Stand up for bubby SD needs to learn this behaviour is not acceptable . Or lots of reminders of how to be gentle ! Good luck she is only young and will hopefully grow out of it .

I would watch her closely, but continue to stay on top of all her jealousy. To make her behave and interact is the best, if you can stand the continual hassle. She will grow out of this as soon as she starts to school and interact with children her own age. The other "normal" is she has short time at your house and she probably feels left out of the "family scene", only because she doesn't live there all the time. This is all a normal reaction for sure. I would not put a great deal of drama into it and just watch your baby.

Do you know another child her age; maybe you could have another child (her own friend situation) come play with her and have their own time.

When my oldest was 4, he was at the stage of wanting attention all the time. He was jealous of his younger brother 1. As soon as he started to school, age 5, he changed and had his own interest and friends. I had neighbors with children the same age. I would invite them over and when 4 years old had boys his age, he was good.

Just a suggestion, it's been a long time since I've been there; but with that said we have grandchildren and notice the same behavior.

Hang in there, sounds like your DH is backing you and that is 3/4 the battle. Good for him and good for you for looking for solutions. Good parenting here.

You are absolutely right that the routine of the household should not collapse because a Princess Has Arrived. I commend you heartily. The girl is getting fantastic lessons in being part of a family, a team, a real human not a gilded speshul snowflake. Brava!

It is unlikely to happen but I have resolved that if DH and I ever had a baby this child would never ever be in the same room with my SD17 without being glued to my side. The risk of harm is nearly 100% so, no, not going to happen.

The incidents you describe are serious enough that I suggest you adopt the same policy. I think your SD is more an average 4 year old than a holy terror like my SD is but 4 is big enough to do some damage when acting out her 4 year old emotions. Take baby with you wherever you go when the girl is present.

Keep that policy until both kids are older -- the one to be more mature in her emotions and behavior and the other to be less vulnerable.

The asking "daddee" something every 2 minutes may be an excellent opportunity to teach her counting and to tell time. Have her do what you did: count up the time she says it and how many minutes have passed. Make a game of it and include other things to be counted.

Increase the time period as you go along. Such as !. Ask Daddy something once every 2 minutes 2. Ask big sister something once every 2 minutes 3. Ask SM something once every 2 minutes. Next week: 1. Ask every 3 minutes. Third week: Ask every 5 minutes (tell her how fast she is learning you are going to skip a week!) Get creative and mix in re-directing ideas so it's not all just "asking." Tell her to "run down the hall" every 10 minutes, count her dolls 2x a day, etc. etc.

It's just an idea but I would try something like that to help her grow in a direction that benefits her and also benefits everybody.

My 2 cents. THIS was a huge lightbulb moment from my dh and I way way back when.

Visitation is the term we can thank family courts for. Anyway, Visitation is NOT designed for the red carpet, special ME and DADDY time or anything remotely like the 2nd coming has arrived. It is for normalcy within the home.

IF Dad mows the grass Saturdays at 1pm so be it, he mows the grass. If SM starts laundry at 10am, and the kids sit in PJ's watching cartoons and ride bikes at noon so be it. IF everyone plays soccer or has dance Saturdays at 11--well guess where you are, at dance. NO special accomidations period.

The problem IS hearing from an ex "oh you don't do anything with snowflake" and bammm all hell breaks loose and before you know it the entire family is UP side down scramming to entertain where no entertainment is necessary IT is however started by one single puppeteer in a lot of broken homes for anyone who falls for it.

Your step daughter is harming and that should be reported with a child Psychologist. NOT a LCSW Licensed Clinical Social Worker, NOT a family therapist but a Dr in child psychology. This is not about her fee'fees or maybe it is. In any event the last thing you need is an accident where the baby is hurt.
DO NOT LEAVE her alone with this baby.

Come on HRNYC---really?

And,

OP I am gonna give you a huge break with the "stfu" comment pointed at a kid because I know your upset. WRONG WRONG WRONG to write that stuff.
JMO
.

***ADD****

also, try to remember she is only 4---the divorce and break up of her family is hard on her. Add into that mix your arrival and your children. Doesn't matter when you starting seeing dad.

BUT hurting anyone is never ever ok. Interrupting IS child like however, She will quickly learn these basic things in Kindergarten IF her MOM and dad don't teach her at home.
Heck adults interrupt and it is down right rude.

Hogwash. This child was a loving well adapted kid, blending well, loving her SM and both her two stepsisters. No one was 'doting' on the weekend kid. No one rolling out red carpets. No one ignoring SM and their kids... Until :

OP on 12 Nov:

"She can not want me around all she wants as she ages but it won't matter a damn bit lol, this is my home. And my children's' home. Majority rules lol. What's good is that DH is aware of all of this (he's been reading step family issues like I have been) and he's prepared. I give him fake scenarios and he responds fairly.
The One who pointed out that she's insecure about her dad- yes,
For sure she is!! Bm told her that she will never have more children because she loves her the most and that daddy doesn't love her the most because he had a new baby. (Wtf!!?) SD told us that when she was 3.5, no way she could make that up.
BM told her that daddy has a new princess now (me) again wtf?!?!
He does his best to assure his daughter and she usually is well adjusted and happy. She shares a room with my daughter and everyone gets along well. I don't have that feeling of wanting to hide when she comes (although from age 0-6 mos I did NOT want her around my son and I still don't know why, and if someone says he resembles her I say NO he doesn't!)"

BM poisoned the kid's head, SM pushed SD away (for reasons she admits she has no idea as to why) and Dad started laying roles in scenarios that weren't actually existing.

And the OP wonders "why is this happening all of a sudden"? *SMDH* OP went on and on and on on everything was just rosy, happy, wonderful 'all one big family'.

SO while you're busy reporting "child Psychologist. NOT a LCSW Licensed Clinical Social Worker, NOT a family therapist but a Dr in child psychology"...be sure to report the role BM and SM BOTH played in isolating this child. Op has numerous forum post, read them.

I find it interesting that SD-4 appears to have no issues with your two elder daughters doing things with your DH and only manipulates when your 10mo old is having Dad time.

It seems to me that this kid has a bit of a manipulation problem associated with no longer being the baby. From what you said in your OP your DH spends a significant portion the time that SD is in your home with her. EOWE is not a huge amount of time but it is regular and since it is regular SD should be held to the same behavioral standards (in an age appropriate manner) as any other kids in your home.

I would surmise that an effective way of dealing with this behavior would be for your DH to put her in her room alone for an extended period of time when she injures the baby. Not just a few minutes. Make it half a day. All while everyone else in the home goes about their normal business. If your two happen to be there... so be it. Then DH can jump in with the lecture about how she is the elder sister and cannot hurt her baby brother and ... if she does it again she will stay in her room (except for meals or if the family goes out somewhere) until she leaves to go back to her BMs.

Lather, rinse, repeat.

She will get the message or ... not. Either way she is held accountable for her choices.

Good luck.