I assume her parents know? Since she's going to therapy and all.
It really is a complicated situation, and there are heavy consequences if you choose to confront or avoid it. The only advice is I can give you so far is, spend as much time with her as possible, be there for her, monitor her behavior. Depression is very erratic and there is no telling whether she decides to cut off her life too, you better take care of her and watch closely to see if it gets worse.