This parent found a nude image (and so was checking the phone?) and took action - she told the school and was told the school wasn't going to do anything; she pulled her child out of school and homeschooled.

I don't understand how you read that and say that she was giving all responsibility to the school. (And the school acts in loco parentis - they're supposed to be responsible for the child for the 6 hours a day the child is there.)