Hi, welcome to the forum. Keep in mind that I am not an attorney but simply trying to offer some ideas.
Just because an attorney says something doesn't mean it is a fact. I would find out if you can have a private evaluation and she can have a court ordered evaluation. I would keep calling attorneys until I found one willing to pursue this if it is within the law where you are.
The situation is that sure your x might take a hike for awhile but the curve ball is you will never know when she wants to come back and "claim" your child. Usually it is for reasons to make the new people in her life think what a great mom she is.
So, first of all find out about court psych evaluations, any attorney should have that answer. If you need a referral I have a great Dr. in Calif. I don't suspect the evaluation will be cheap but may be well worth it if the courts allow it. Then it could become the battle of the shrinks and hopefully you have a better one than she will get via a court referral.
I am very sorry you and your daughter are in this horrible situation.
You can email me for the contact Dr. in your area if you can pursue that firstname.lastname@example.org