She is very careful with her electronics, and she actually keeps her keys on a clip hanging outside her purse to keep them from scratching her iPod. The purse was sitting by itself in the seat behind her. She said it frightened the life out of her when it cracked and described the sound as a "shotgun" going off (which i personally think is a bit of an extreme description). I don't see how she could accidentally put anything heavy enough on her purse to crush the screen either way. The apple store actually commented on the fact that the iPod touch was in pristine condition and there were no signs of impact damage causing the fracture to the screen.
She had almost had it for a year when it broke, she had purchased AppleCare and the extended portion had not even kicked in yet. So they transferred the AppleCare to the iPhone for her.