Well I made a post here not long ago and it didn't get any replies, so I thought I'd reply to yours in case you don't get any.
It's possible she didn't know for sure she was having a heart attack when it happened. I could be wrong, but I believe I've read that women experience heart attacks much differently. Either way, all the questions you have would best be answered by a doctor, of course. Do you live near your mom? If so you may ask to accompany her to her next cardiologist's visit.
As for sites, webmd has actually been pretty informative throughout my dad's ordeal, and even the wikipedia has surprisingly good medical articles. Those would be a good place to start as there are references listed and you can also visit those. The American Heart Association would probably have some information concerning warning signs and prevention, too.