HELP! My sister just got hit in the head!!!!!!!!!!?

My sister was sitting in the hot tub and the cover (one of those foam ones, but it weighs quite a bit) blew over on her. It hit the front right side of her head about three inches from her forehead on the top of her head. She says she's fine, but she doesn't ever tell when she's hurt. She won't let us get her ice for it. Should I be worried?? What do we need to do? How do we know she's not going to drop dead like Natasha Richardson??