Ghost Girl

Ghost Girl is a ghost-like monster roaming the Haunted Mansion. She has nothing to do with Chrome's plot whatsoever, and acts as merely a hindrance. Chrome also mentions that Ghost Girl simply wandered into her territory.

Alice says that a Ghost Girl and ghosts themselves are different from one another because a Ghost Girl is born from a collection of souls mixing with magic power. Luka questions this, implying that he thinks it is more likely that Alice is simply making excuses to avoid facing the possibility that the Ghost Girl might in fact be a real ghost.

The difference between the Ghost Girl and actual ghosts becomes clear when Alice faints from having seen the real ghosts after Chrome is chased off - she realizes that these ghosts are different from the Ghost Girl.