I think you should try it but in school time.The holidays are different and fun things will be arranged.
Agree with this. If she’s going to see what it’s like to live there it should be including after school clubs while he’s at work, helping with chores, etc not 6 weeks of no school and the novelty of her being there for him without her having to do any chores or homework etc
I agree with others though, that all the change over the last couple of years is probably why she’s so angry and that this is just another change, which could make her feel even more wobbled.
Long term it might help, as she’ll see that this isn’t the magic answer, and just giving you a break from it would be useful. But it could equally mess her up even more, when she feels like you don’t want her around any more (no, she won’t vocalise this, but it will be there in her mind).
Also this: Also your ex should be having both girls for half the summer holidays plus half the school holidays in general. It isn't fair for you to manage childcare on your own..
He needs to be pulling his weight regardless so if it means a move more towards 50/50 rather than being all you or all him, it might be good for her. Then dad’s house isn’t the novelty, they’re both home.
I do think that if your DP moved out your DDs behaviour would probably change. Moving from one step-situation to another when she’s already dealt with so much may not be the answer here. Both of her parents putting her first before their love lives would undoubtedly help her. You can’t control your ex but you do have control over who lives in your home with your DDs.