Geraldine is the fianceé of Laszlo that has been kidnapped. The Hero must rescue her in the side quest Kidnapped if the Hero is male. However, if the Hero chose to spare Elise at the beginning of the game, then she will appear as Laszlo's fianceé instead.
Near the end of the quest she will give you a choice for her to dump Laszlo, stay with Laszlo, or say nothing. You can also not press any button, and the result will be the same as saying nothing. If you tell her to dump Laszlo, she will inform him that she is leaving him during their conversation at the end of the quest. However, the Hero cannot marry her later and the quest A Lost Romance will not occur.