It's horrible the things people do to themselves when they feel that they've failed at something I think it's that she thought she didn't live up to other people's or her own expectations, and felt like she was a failure, which of course she's not.

This happened at my high school when I had my a-levels. A guy in the same year got worse marks than he wanted, so he shot himself in the mouth with a rifle. He left a note behind saying something about failing, and an apology. He didn't die but had a severe damage in his mouth obviously, and was in intensive care for a long time. I don't know how he is nowadays, it's been years since this happened. I was shocked at how people can react to these things

Of course this is worse for you since the girl is close to your brother's gf... And for your brother's gf it must also be very bad, seeing her friend like that Can't be very easy...