Good for you for insisting on a third party being present. She won't go for it, of course, because she's trying to bully you into what she wants.
And yes, definitely consult with a lawyer about your rights regarding the kids and the therapist. I don't know anything about that area of the law, but it seems weird to me that a therapist can see a minor child and keep one of the parents completely out of the loop - that doesn't sound right. And as best I know, doctor-patient privilege with minors only applies to treatment for STDs and sexual issues like birth control in my state.
