How has she been since? Has she been happy and alert or does she seem drowsy (more than usual before bed). If she is relatively happy and the mark has gone already perhaps it wasn't hard enough to do too much damage, my DS is constantly crashing in to things and it is always his head that he hits!
If you are really worried give nurse on a call a ring maybe they can triage her over the phone and put your mond at rest.
Good luck hun hope she is okay xxx