Can i still take lefal action against school and MIL

My MIL is not welcome in our lives. A year ago she took my daughter from the school. She was not allowed to. The school never realized it on their own. My husband said he would handle it. He never did, now his mother is contiuing to have unwanted contact with my children at the school. And the school won't stop it from happening. She also knows people inside the school so that has allowed her to do what she wants inside the school. Police won't help,me. I need to know if it is too late to do something about her taking my daughter from the school a yr ago, since that seems to be the only illegal thing she has done. About 5 months ago she waited at the school to approach my child on the bus to give her candy. The school resource officer did an investigation and told her to leave my kids alone. But she is continuing her behavior. I need it to stop before she removes one of my kids from the school again.