Worried about girlfriend's alcohol intake

I'm worried that my girlfriend has been drinking a lot frequently. I'm not saying that she's alcoholic but if not stopped, she might go down that path. It all started after her parents divorced. I thought it wouldn't affect her since she's not living with them anymore and has not seen them for a while but I was wrong. When her mom called she just broke down and things have never been the same. Her brother's still out there in some interracial date tour so I can't really talk to him about his sister's situation. They talked over the phone but that's it. I don't want my girlfriend to spiral down a dark path especially with alcohol involved. I don't know what to do.