This girl in my class copys other people's exams and never owns up?

In our summer exams as they are small this girl is copying of the person next to her and I want to tell but I think I will sound like a snitch and she never owns up to anything like she will litter then say it wasn't her and I don't know if I should tell?? But I feel sorry for her as she has no dad and she apparently has fights with her mum??