What can we do to help our kids?

My husband has 3 children from a previous marriage. The oldest lives with us, but only because we won custody of her a little over a year ago. My step daughter told her lawyer how badly she wanted to live with us. That combined with my step daughter having anxiety and panic attacks and the mother refusing to put her in therapy got us custody. But the court didn't feel it was necessary to remove the other two. Now my husband and I are worried about the middle child. She has a lot of anger, and even the school called the mother about putting the child in therapy outside of school. The mother has yet to do it, and my step daughter is getting worse with controlling her emotions. We have joint custody, but mother has physical, and in NY physical custody lets her have final decisions. So we can not put my step daughter in therapy without mothers consent. We want custody of her, but are at a road block. School has to wait until she has another explosion at school before they can do anything.