How can I help my stepdaughter?

That's a really hard situation. Something simialiar happened between my father's rights to his son's learning/special cles (who has a learning disability) and conflict with my mom. Now I can't give you a perfect answer because I don't know much about court and such... But, have you tried to just talk to the mother. I ume she wants what is best for her daughter too. Why do you think she stopped taking her? Was it not suitable for the child? Try to understand her logic and why she is doing what she is doing. Also, can you speak about this why someone more familiar with the case? Do you have a lawyer that could help? Good luck with your situation! :)