I feel for you, I'be had a similar situation. except my SS is much older.
Keep in mind a lot of that just comes with being three, all three year olds will test boundaries to the breaking point.
Also,at 3 she's still young enough to recondition, it will just take time and patience to reteach and reinforce good habits and rules since she has been allowed to get away with so much.
make a plan with your DH to help her relearn behavior AND STICK TO IT. Agree upon rewards and discipline.
I find that the STAR CHART really helps with little ones, I have a 3YO as well.
Explain that stars are given for good behavior days and doing all the necessities, i.e. brush teeth, going to bed, etc. And once she reaches so many stars she will get something that you and she agree upon. Maybe a book, or a trip to the zoo, or a special toy.
A lot of people will tell you not to reward, but I find that it works in family, so it's just a suggestion.

Edit: My bs also has tried the throw a fit and scream until you comply thing.... I leave the room.
when he becomes insistent and whiny and starts to cry and scream with the "I don't want to" I put him in his room. "You're in time out until you are ready to act like a big boy/are ready to eat your dinner/ask nicely/etc." Always reasonable requests. He used to kick and scream and cry, eventually once he realized I'm not coming back he stopped. When he came out I ask him "are you ready to xyz". By then he was calm and said yes ma'am. Otherwise I sent him right back to his room where he would perhaps do it again, and eventually comply. It gives them times to calm down and consider what's being asked of them. I've used this about 4 times now, and the fits are almost non existent. if I do send him to his room his tears don't last long and it's not a huge blow out fit.

Hello, my stepson is also three. I've been in his life for over two years (since he was 8 months). His mother is more apart of his life than your skids BM and he sees his mom regularly 8 days a month. Now on to your post,I think most of her behavior problems can be from her age. The dreaded "threenager" that being said though, my SS does not act the way you've described yours. But that's probably because me and my DH have been raising him together for the most part. When SS is told no and he reacts with a tantrum, we give him two options: one is favorable and one is not such as "would you like to stop throwing a fit now or go to bed?" 98% of the time he will choose to move on and go back to playing.

The idea is to establish that you will not tolerate tantrums for attentions. And it sounds like your SD is doing a lot of that. If she is screaming, have your SO pick her up and put her in her bed and tell her she can get up when she is done then walk out the room. We had a little spout of "fake crying" sessions around 2&1/2 with SS and I would send him to his room. He would just wail louder so I would just get up quietly and shut the door. It's okay if they get up and start playing in their room, the goal is for them to move on from the tantrum. My SS would stop faking it once I shut the door to come open it, then he would go play with his toys quietly or ask me if he can come out again. At 3, they just want to be seen and heard at all times (nbd right? Hah) so the biggest punishment you can give them is taking away that attention when they are misbehaving. I promise it's a thousand times more effective than spanking ever will be.

Now here's some advise I learned here, don't EVER touch a kid that's not yours. And I say this not because I don't agree with spanking, I do for dangerous misbehavior (running from parent in parking lot, playing to close to the road, etc) but SKids and confrontational BMs have a wonderful track record for calling CPS on stepparents...don't believe me just keep reading some of the blogs here and you'll see. Plus eventually she'll start to weigh the worth of getting what she wants versus the temporary sting of a spanking, understand? My DH told me his mom spanked him as a kid (my own had a policy similar to mine and I was spanked maybe once or twice as a kid) and he would just do what he wanted and take the spanking because that meant he still got what he wanted...yeah you don't want that kind of stubbornness to grow in your SD so try another route for punishment.

Hindsight is 20/20 they say so I am going to disagree with the suggestion of doing a rewards system with a 3 year old and I'll tell you why: we used this technique (?) for SS3 and are having to fight it now. He is a great kid no doubt but now he thinks he should get something for everything he does. If we go to the grocery store and he's well behaved the whole time we are there, he expects to be rewarded. If he goes to poop on the potty (potty trained since 2 on a reward system) he expects to be noticed and praised everytime. It came to the point where he expected rewards for simply doing everyday normal activities that he should be capable of doing. Not his fault, ours as parents. The reward system worked amazingly for behavior but no it's set a precedent that good behavior is rewarded when the reality is that good behavior is EXPECTED. We've been breaking our own habit of treats/rewarding him and it's a little rough. I can see his confusions for not be rewarded but he's catching on.

I hope some of this helps some, I'm on Stalk for psycho BM problems so not so much Skid problems as of yet. There are others here that may not have 3 year old, but have been through this phase that can give you better help than I can.

First of all, Welcome!!

I'm a stepmum to SD11 & SD16 year old and a BM to BD14. I've been with my DH for over 10 years so I've BTDT and have the t-shirt...

First of all, 3 years is the most trying age. They totally push boundaries. I remember an incident at a local box store where we said no to a toy and she literally threw herself on the ground kicking and screaming. When DH picked her up to get her out of the store, she started screaming help! mommy! like my DH was kidnapping her... We had store security following us, our other girls sooo embarrassed, seriously a nightmare event. Ug!

I'm not a self help book person, but I got a book, How to Behave So Your Children Will Too! The book itself is actually pretty common sense stuff and funny as heck!! The big thing is kids want attention, positive or negative. When they push boundaries, stay the course!! They will test you and if you give in even once, even if it's after a long period of time, they will learn to just wear you down and it gives them a frame of reference and timeframe...

We did do a rewards chart. It was smiley faces and after they got so many (like 10, i can't remember the number truthfully), they got to pick from the "Treasure Box" which was a box of things from the dollar store. They could lose a smiley for poor behavior as well. We started out with basic things then shifted expectations to going above and beyond good behavior.

Good luck with your SD3!

I would totally agree. I don't know who came up with terrible 2's but it should be terrible 3's. The most important 2 things about parenting especially in a step situation:

1. Be consistent with the punishment. That means no laziness. If the rule is she gets time out for doing something wrong, she gets time out. No ifs, ands, or buts. Period Dot. That means a lot of getting up and doing the work. But consistency is the only way to break this behavior and make no mistakes - you must break this behavior NOW!

2. Your fiance MUST have your back on all matters. You two need to communicate about the ground rules and both be concise on them EACH time. Do not allow a child to run the household. They are children. No precious little snowflakes. They must learn now to behave and obey the rules. It will break your heart. It will fill you with guilt but you both must be on board with the same game plan. No spoiling. That does nothing for a child except teach her to manipulate.

Also as a side note- I don't agree with rewarding a child with food ever but especially with something that should be done anyway. Going to the mall and being good is just something you do. If you don't you get punished. You don't get rewarded for doing the things you should do anyway. Secondly, I would add that she needs to be eating a healthier diet. That means throwing the snack foods out, if need be and not having them in the home. We don't have snacks in my home. We don't serve juice. I sometimes allow my sons to have a granola bar before bed or something small like an apple or banana. Teach these habits now.

You are in the very good position of having her early and full time. Take advantage of that by being good parents. And if that means going to classes (I sure did when my husband and I divorced) then do it. It's a very difficult situation and BM will make it difficult at every turn. DOCUMENT EVERYTHING WITH HER. Keep a written log (Judges love that stuff) and if she ever does fight for custody have it all organized and ready. Education is the key to winning any war. Good Luck