Hi Bauers !
Sorry to hear about this.
My ex partner wanted to be friends as well. She knows about her problem being BPD, and denies it.
Although one moment she actually talked with me and agreed she had a serious problem, but external influences destroyed that. Someone with his own agenda, very probably NPD. Or just a very big selfish character.
I offered her to go both to a specialised therapist and see which problems we both might have (although I already knew about my own issues) she rejected the offer.
I told her I only wanted to be friends with someone who was willing to change it's life, make it a lot better. She refused.
In one mail after that she told me that she understood that I didn't want to be a witness anymore about the fact that she was destroying her own life and that I still had love for her (not being in love anymore). She did hit is spot on, but she denied again to have BPD... .
Point is, you know she has borderline, she is not going to change, change comes from within, acceptance of the problem and the willingness to do something about it. She does not do that.
She was a bad and toxic lover. What could make her a good friend ? Nothing... . Sad, I know, but a fact.
You've experienced it now. It does not change, it will never change, unless she is willing to change.
If my ex would contact me again and say she is accepting her problem, I would see it as another way to try to recycle me. Nothing else.
Starting therapy may even be a trial for recycling. You don't know what the motivation behind it is, and it can be the complete opposite of what you may hope... .
Knowing your situation, may I ask you this ? What is more important ? Being friends with someone who doesn't wants to be friends, but wants a recycle and destroy your life even more ? Who is in denial of her problem ?
Or being there for your kids and letting go of the toxic situation which is never going to change and cause more pain and havoc in your life ? And to give you the time to heal ?
Remember you have a choice !

Hang in there !
Reg