That was a lot for a 16 year old to deal with. Also a lot for you as a friend to try to understand and come to grips with. She sounds like she was vulnerable to begin with and the death of her grandmother and the dumping of her bf probably took her over the edge. That would be a lot for an adult to deal with much less a teenager.

Know that she is getting the help she needs and you only have to let her know that you are there for her. Let her talk if/when she is ready. She may be embarrassed or uncomfortable.

This is just my opinion, but I feel that when a person reaches the point of wanting to take their own life, they are in a selfish mode. They aren't thinking of others. That's why she didn't confide in you. She also may have thought you wouldn't understand. That doesn't mean she doesn't think of you as a friend or value your friendship.