Surprise Party Ideas for a 13-year-old girl?

I am having a surprise birthday party for my sister who is turning 13. The only trouble is, we are have a heck of a time trying to figure out what the girls should do at the party. There will be 7 girls there total, counting my sister.
Help please? I really want to do this for her.
Answers:    Sleepover
Go to your local pool
Spa themed- Facials, manicures, next do hair, makeup
or you could have a disco theme, and enjoy mock-tails, dancing, music
or an old fashioned party near fairy bread, pass the parcel, musical chairs, and loads of baby similar to food--the kind of party you have when your 3 (my friend did it and it rocked)
Go to an arcade
give an account everyone to dress up and have a themed party
if i think of more bad edit
Good luck

Edit:
(i though of more)
You could get all the harry potter movies and hold a HP night, you could get the quests to dress up and later once all of them have been watching contained by order take them to the movies to see the new one
Get a bunch of stickers and undecorated hat. And feathers and anything else you can think of and they they use their imagination.
Also any other kind of kraft teens love.

Related Questions:
What would you do if your child get pregnant/impregnated or have a pregnancy startle?   When she say yay and OMG, do you discern resembling throwing a bucket of dampen over her?   I'm really hurt and i don't know what to do please give a hand me *10 POINTS*?   Whats your style? what do you ruminate the most defining entry contained by fad is? what rage style do you dislike?   How come,even if you've never see,or read,something,you know what it's roughly speaking?  
  • How do I convince my mom?
  • Should I put in the picture my mom roughly speaking my boyfriend?
  • Hormonal Imbalances Much?