Mouse is the name of the girl. It is also the name of her friend who perches on her shoulder. It doesn’t cause as much confusion as you would think, since non one speaks their name aloud.
Mouse was very shy when she was alive. Thats how she initially earned her nickname.
Now that she is dead, her bashful behavior has increased. You probably don’t even know you’re being haunted. She stays completely out of the way and haunts you very very quietly from inside the walls of your house. She peeps through mouse holes and cracks in the wall. You are strange and fascinating to her. She’d love to talk to you some day, but she hasn’t worked up the courage yet. For now she will do all her socializing with the ghosts of the mice that have lived and died inside the safe haven of your walls.