Because most of u on here are ex wives/gf’s who feel superior right?
Nope. I'm current (first actually!) wife, no kids, while DH has ex-DP who is the mother of DSD. So I'm usually good for at least seeing the SM point of view, if not sympathetic.
I agree your DP's ex's behaviour sounds crazy - but PP's are right, her previous behaviour is really nothing to do with you, and something that shouldn't really still be a conversation in your house - it's affecting your relationship, and you shouldn't let it.
Regardless of what I think of my DSD's mother's behaviour or life choices, it's got absolutely nothing to do with me, and I have to respect that she's DSD's mother - so even when DSD is angry or upset with her, or in a particular moment she doesn't want to go, I know she still really loves her because she's her mother. She'd need to do something pretty catastrophic to break that bond. (And FWIW, I'm sure there are times she also says she doesn't want to come to us! Typically focussed around not wanting to leave whatever she's doing at that particular moment.)
If or when I do have opinions on parenting type things such as screen time allowed / leaving with grandparents etc, I try to keep those opinions to myself for that reason. She's her mother, not me, and it's up to both her and my DH to discuss / agree what they see fit in terms of their co-parenting. While I do have a big role in her upbringing, particularly when she's at our house - and we have a great relationship - again - I'm not her mother, so it's not my place to judge DH's exgf's decisions, parenting or otherwise.
I listen if DH has a particular issue with something she's done or said relating to DSD that he disagrees with, and if he specifically asks me for my view or advice on something I'll of course provide that support - but I would think worse of him were he to properly bitch to me (or anyone) about the mother of his child, or not at least try to defend her if I or anyone else went off on one about her.
I just think it's worth some thought - I can see it's frustrating for you and it's easy to have an opinion, but would you want to be with someone who would openly trash talk the mother of his child, regardless of what she's done?
This woman is going to be in your life regardless, if your relationship has a future. You need to decide if you can make peace with that - life will be easier if you can all get on and you can let some of this anger go.