What do you do if you suspect child abuse but arnt sure?

my friends girlfriend has a mean grandma. i didn't think much of it at first and just dismissed it as over-protectiveness. but ive been chatting with her and when they saw her grades weren't very good her grandma called her a "f*#& up" and things of that manner. her dad was also yelling things that, im sure, didn't help her self esteem. she chatted with me soon after, which is how i found out, and she said she was on the brink of tears. Later in the chat she told me back in 6th grade her grandma used to hit her, she also said her grandma almost hit her a month ago just because she looked at her wrong. during the chat she changed her status to "why wont she just die". I tried to tell her to talk to the school councilor about it but she just said theirs no point in it. what should i do?