I think she committed suicide because look who she was up against. Cato and Thresh were strong male competitors. She never she could never beat the star crossed lovers either, so she decided to take her own life.
omfg!!! every one in the theater was laughing sooo hard (along with me)!! When i was reading the book i was like, "they are gonna leave that out of the movie" and when i saw the movie i was soo suprised!