The mother chose her path and her child will have to live with the choice. Hopefully, one day, she will wake up.
It would appear the mother did try to have her daughter go down a different path by signing her up to a Christian school in the first place. That was a positive step for the child. What could be better for the child than associating with other Christians (besides the obvious regarding the mother)?
I don't claim to know many of the facts of this story but on the surface of it, I would bend over backwards to try to keep the kid in a positive Christian environment in spite of the mother. It does sound like the school has made an effort on this front as well. I just feel bad for the kid…