Hold an Auction
Tell each girl to bring an item to the party that is in good shape that they don't want anymore. The item must be wrapped so that nobody can guess what it is. Make some fake money ahead of time and pass an equal amount out to each girl (for example, $100). Auction off each item and don't allow it to be unwrapped until someone wins it. Throw in some mystery gag gifts to keep them laughing. At the end of the auction girls can trade their items or buy items from each other with any extra money they may have.
Telephone
This classic game is fit for girls of all ages. Create some pre-made cards with phrases on them and give one to each girl. Each girl takes a turn whispering the phrase on her card into the ear of the person to her right. That person whispers the phrase to the person on her right and the pattern continues until the phrase makes its way around to the last girl. The last girl to hear the phrase says it out loud. The girls will hear how the phrase has changed from the original, and everyone will want to chime in with what they thought was said. Start the game again with the next girl and a new phrase card.
Freeze Dance
Freeze dance is another game girls of all ages can play. You can make it age-appropriate by your choice of music. Gather the girls into a room, turn on the music, and have them start dancing. As soon as the music is turned off they must stay frozen in position. Anyone caught moving or not freezing fast enough is out. The last dancer standing wins. Add some unpredictability by turning the music on and off quickly or keeping the music on for a minute or more at a time.
String Relay
Tie two spoons or similar object to the ends of two balls of yarn. Line up the girls into two teams. Give the spoon and yarn to the first person in line on each team. Each girl must drop the spoon down her shirt and then down her pant leg and quickly pass it off to the next team member to do the same. When the spoon gets to the end of the line, it must travel back to the beginning again in the same way.The team to get their spoon back to the beginning of the line first wins.