For the same reason I can barely remember the names of the Presidents, but I can remember the details of every truly bad argument I've ever had with my boyfriend, down to what we were wearing, who was standing where, and what was playing on the radio in the background while we were arguing. It's why probably everyone in this room can remember what they were doing on 9/11, or (if you're older) what was going on in your life the day Kennedy was shot. The heat of the moment sort of emblazons the details in your mind.
But it sure doesn't sound like she had any idea of the seriousness of the event at the time. She only found out some time later, since per her she doesn't even watch the news. And Trayvon was not her boyfriend.
So why would it stand out?