Some good birthday gifts for a 12 year old include Scene It game, Ugg slippers, Giftcards to Abercrombie, Hollister, American Eagle or Aeropostale, Jewelry, Klutz craft kits and iPod Nano. For more ideas, go to http://www.squidoo.com/gifts-for-12-year-old-girls.
Jewelry and lip gloss if she is girly. If she is really into music get her band merch from her favorite band. Maybe also some CDs from her favorite band. She might also like nail stuff like nail polish. if she had an iPod iTunes would make a great gift as well and so would gift cards