Scary Scavenger Hunt
Before the party hide scary items around the house or yard. These could be fake spiders and snakes for younger girls, or scarier items like pretend severed fingers for older girls. Play in the dark with torches and award a prize to the girl who finds the most scary items within a set time frame. Play spooky music while the girls are searching.
Torchlight Tales
Have the girls sit in a circle. If possible, make a bonfire outside and gather around it. Have the girls wear Halloween masks and disguises. Pass a torch around the circle. Whoever is holding the torch must hold it under her chin and shine it up at her face as she tells a scary story or spooky experience. If the girls don't want to make up stories, have some printed for them to take turns reading out loud. Have an adult dress up in black with a scary mask and creep up on one of the girls while she is listening to the story and scare her. The girls are sure to all join in with her screams.
Body Parts Game
Before the party prepare a series of boxes to place gross items inside, labeled as body parts. Each box should be large enough to place your hand inside comfortably. Cut a hole in the side of the sealed box; make sure the contents are not visible. Label the boxes with body parts, then place items inside to resemble those parts. For example, fill the box labeled "intestines" with cold spaghetti and the box labeled "ears" with dried apricots. Give each girl a piece of paper and have her feel inside each box. Let her write down what she thinks each body part is really made from.
Alternatively, read a scary story and pass around body parts to accompany the story.
Murder In The Dark
Hand each player a slip of paper. One should read "murderer," another "detective" and all the rest "suspect." Each player must keep her part a secret. Turn off the lights and play some spooky music. The murderer must find people, tap them on the shoulder and whisper "you're dead." If a suspect is tapped she makes dying noises and falls to the ground. If the detective is tapped she says, "murder in the dark!" When the detective is killed the lights are turned back on. The dead suspects remain pretending to be dead. The detective surveys the scene, then guesses who the murderer is. If she is right, she wins, but if she is wrong, the murderer wins and must reveal who she is.