How to get rid of lice?

I need some ideas on how to get rid of lice. I have tried over the counter treatments it goes away she goes to school and gets it again. I’ve tried straight tea tree oils hair spray and gel to prevent but she just keeps getting it. I have washed and treated everything she and her sibling have. I’d like to add I have 3 kids at home and me and dad all with long hair and she is the only one of the 5 of us getting it which is very weird to me. Any suggestions would be greatly appreciated