So Claire loses her job for sure here after this

She's a teacher and he's a student. Yes, he wasn't a student when they had sex, this is true and he was at least 18 (I think they allude that he is 19 in the movie). So there is no legal problems with having sex with him. However, think of it this way. There is no way she keeps her job. The school would not want that on their conscience. She helps the guy get into her class that she had sex with. Yes her computer was hacked but she would have to prove this. Then the guy does the graffiti in the bathroom, something that for sure would have at the very least been looked into a lot more.

Then he kills the Vice-Principal, lures her husband and son to the ranch and lures her too. There would have to be plenty of explanation as to why a student would do all of this. Not saying she wasn't justified in killing him because she was, but no doubt the school would connect the dots and realize she slept with a student.