Sorry to hear about your loss, it is likely to have been stress that killed her.
The same has just happened to me, my guppy just burst, litterally, it was not a very pleasent sight at all. I didn't think she would have been close to having her little ones, her birth canal never seemed to open up at all. She was ok last night and this morning, this evening when I got home from work i went to check on her and she was dead with her belly split open.
urg.
Kaz