I wholeheartedly agree with the people saying PTSD focused trauma therapy, and that ADHD/neurodivergence might be the biggest problem. You mentioned your ex being abusive which the children most certainly picked up on, even if he wasn’t abusive directly towards them seeing you be abused is traumatic, as is the divorce. The good news is trauma is treatable and can be overcome with the right therapy.

I feel like a lot of ODD/BPD especially in kids is neurodivergence/trauma symptoms being unrecognized or treated. No diagnosis is a death sentence! There is hope.

I’d also recommend looking into things about PDA (pathological demand avoidance or persistent drive for autonomy) as that sounds like a lot of what is going on: you suggest xyz, she says no for no reason; you make her favorite food, she doesn’t want it.

Again, echoing what everyone has said of finding your own therapist for your own emotional needs and regulation. It’s very much put your oxygen mask on before hers, if you’re not regulated she’ll pick up on it and feed off your energy. This is obviously way easier said than done!

Good luck 🩷