I guess she tripped going up the stairs and bumped her forehead between the eyes. She's fine - running around, playing, acting goofy, but it sounds like the bruise is EPIC. I might carry a copy of the incident report around with me for a while if it's as good as I think it's going to be.
EDIT 4/26: Well, either they're much more alarmist than I, or the egg and bruise went down as fast as it came up. By the time I saw her (around 7:30,) if I hadn't been forewarned I would have thought she had a slight smudge of dirt on her forehead. I'm pleased. She told me that she got a boo-boo, and that she needs to be more careful. That's my girl.