There are many factors and explanations that can lead up to this, though I'll give some examples:
1.) Short-term memory loss
2.) Alcoholism (slows down your memory an damages your brain's memory function)
3.) Amnesia
4.) She met a lot of new people, and she might have not paid attention to the name when the other person gave it
5.) The party was loud, so possibly her mind was distracted by the music/guests. Not only this, but your thoughts are scattered when there's any loud noise (hence why most people tend to concentrate better in a quiet setting, such as the library, as opposed to studying near a place that is loud like an airport or a construction site)
