So what is your bf doing to parent her? How does he react to her tantrums? Where is he when she throws a fit and what is he doing to curtail it? 

Your boyfriends daughter is 3 or 4, right? 

At that age going to the zoo, maybe a hotel for 1 night would be ok for her, Since she is having melt downs all of the time, . But a long holiday---NOPE I would book long trips when she is not there---for now at least. 

It is OK to have different vacations for different kids needs. Maybe you felt awful for considering that??? Please don't, ok?

Like other posters have said in a few blogs. Maybe it's best to disengage if you haven't already. I have worked with children with a lot of different varitions of behavior. Autism is more in males than females, but I wouldn't totally count it out. I would maybe have a sit down with your S/O about getting her tested for Autism or ADHD, or maybe suggest some behavioral therapy. 

I think I missed how old your SD was? I know that they usually cannot diagnose a child or treat a child for ADHD until they are 5 and up. I know it sucks that your SD seems to have some awful behavioral issues, is it possible this stems from BM's house? I definitely would recommend bringing her to a medical professional first and foremost, and if that's not it. Then I would talk with S/O about discipline and boundaries. 

If SD goes on vacation, let him do the disciplining and try to just enjoy yourself. It's hard with all of the screaming and kicking, but at this point, so you're not stressing out, just disengage. 

To see how she addressed tantrumy unruly kids.

my skids were sd23, ss20 and sd13 at the time and we didn't take them on mini getaways to celebrate our wedding anniversary, birthday or romantic getaways even yearly trip to Australia where i'm from. Nope skids stayed home

my husband in fact told his son 2 yrs ago that due to his behaviour towards us, hubby would not be bringing him on yearly trips to Australia because he made it very clear we weren't family from the disrespect and shunning etc of me and my 2 young kids with hubby and therefore none of us wanted a holiday sabotaged or for any of us to be made to feel unwelcome in our own home

he told ss that this was on him for what? His own mum disowned him over 12.5 yrs ago, he barely has a relationship with his full sisters as they're brainwashed and controlled by bio mum, now he has people that just wanna get along but he chose to be an arsehole for nothing so he needs to ware the consequences of his actions. That none of us want to torture ourselves with his miserable disrespectful presence.

ss claimed it wasn't intentional how he treats us but he knows he actively shuns us and treats us with disrespect which means it is intentional. Hubby told him that he could spend holidays alone and reflect on the person he is but hubby isn't sabotaging a holiday with us for his adult son to come along and ruin it

as for sd's, the miniwives from hell!! Nope, no events/holidays or getaways will they be on. They have no respect for our boundaries and privacy. The last trip had then sd24, bang our bedroom door at 7am wanting to get a bag of sugar from the car to gift to her aunt who wasn't even using it.

sd knew daddy was likely having husband and wifey sexy time as our bedroom door was closed and she needed to make herself relevant. Believe me, hubby didn't get sex for a few weeks because that incident destroyed any intimacy we had and hubby realised they just weren't worth it bringing along to destroy or interfere in our marriage relationship.

if skids refuse to be pleasant, then they don't get to go on the trip and stay home. Honestly, i'd suggest bringing your daughter along only and telling hubby to be home alone with his daughter as none of you wanted your holiday ruined and claim refunds for hubby and sd ticket etc

I put my foot down about 3 years ago after yet another stressful holiday thanks to SD's poor behaivour and decided I would no longer go on holidays (other than a weekend away perhaps) with my skids again. She's much older (17 now) but has pretty much ruined every family holiday we have ever had. One more year until she's 18 and then I hope we can start taking holidays again with my SS15 (who is lovely) and my DS3. 

If she is only 3 or 4 you all should have planned holiday with her age in mind.  Given her past behavior, it seems like you would be asking a lot of her to maintain for a week in a strange place!  

And... you know your BF isn't parenting her well.. so maybe the solution is you take separate vacations with your kids?  Your BF is not your child's father.. so it's not like you are asking her dad to not go with her.  You take a nice mother daughter trip.. and your BF can do a trip with his child.. then maybe you can do things as a couple and both kids can stay with their other parents for that time?  Maybe she will mature over time and more can be done.. but with his parenting.. don't hold out too much hope

Your skid sounds like something is def wrong. She needs to be diagnosed.

Cancel trip until she has been examined. Her father needs to parent her more not less.

Killjoy ruined every single vacation we went on.  We would have been better of not going at all.  If a child is so badly behaved at home, being around her 24/7 will ruin your vacation.  The resentment will ruin your relationship.

Cancel the trip or go with just your child.

This is what your SO's X is for.  Your SO needs to decline visitaiton for that holiday period.  SD can learn that her behavior has consequences.

How iold is this kid btw?

I wish i could opt out of going on holidays with sd. SD always makes our trips miserable. I'm lucky last summer she opted out of visiting us for MONTHS we've only seen her 4 or 5 times since july 1st. But the summer before, she faked a sprained ankle, then when told "oh, it looks like you're feeling better, since you haven't been limping/ favoring that foot", she throws a fit and cries that were calling her a liar (which i was totally calling her out, but i was being super nice, had a nice concerned tone)  the time before, we went to Disney, and she was trying to dictate what we were going to do the entire time, actually that's just how she is in general lol,  so i can apply that to EVERY trip we go on.