My friend is mad at me for helping her?

One of my friends has been being bullied severly on Formsprings anonomously by someone at our school. And I mean HORRIBLE.She's very strong willed so it doesn't bother her. So today at school we had this embly about Internet safety and they were talking about cyber bullying. Naturally I raised my hand and said that one of my friends was being cyber bullied anonomously and I wanted to know if there was some way that we could find out who it was. And now she's FURIOUS with me. She keeps telling me that it didn't bother her and she could handle it herself. Maybe it didn't bother her, but it's still really really mean. She has not been doing anything about it either. I have been treated like crap before and I don't want to see it happen to anybody else, especially my best friend. It's not like I said her name in it, not a lot of people knew who I was talking about. All my other friends think it's crazy for her to be mad at me. I was trying to help her. What should I do?