I am so sorry for what is happening to you. It must be absolute heart break. My suggestion would be to write your ex a letter outlining your legal rights as a parent and the repercussions that your ex will have to deal with if she doesn't do the right thing. Tell her that you have a lawyer and that you will use the law if you have to. I don't know your ex, but hopefully this will scare her enough for her to reconsider what she is doing.
My thoughts are with you honey, and I hope that this horrible situation is sorted out for you and your baby girl.