I agree with everyone else, especially riversong (cool name BTW )
Look, for starters, you only know what people have told you about BM...I'm sure my children's stepmum would have heard all sorts of things about me...all one sided...and probably doesn't think all that much of me either! She's probably smarter than me too! And if she pointed something out about my children, I'd be grateful but that by no means gives her ANY RIGHT...to follow up on or to be a part of any treatment my child needed.
My husband is my children's stepdad...and although I expect him to support me on any decisions I make in regards to the children, I understand that he doesn't have any rights either and I would expect that my ex would be very put out if I tried to include him in important doctor's appointments and things. So it goes both ways.
It's clear you don't like her...I'm sure she knows that...and I were her I wouldn't want you a part of this either and she has every right to feel that way..she is, after all the child's mother!