I don't think it'd ever occur to me to sue a school over something like that if it happened to my kid, I'd want the pedo in jail and if the headteacher or whatever was negligent on his background checks etc. he should go to jail too.
She obviously had nothing in her background. They usually don't. Also, I think nowadays they do background checks. Fuck, they did them for managerial positions that I had, so they MUST do them on teachers!