My dd is nearly 14 and some ideas I would have are:
Things for bedroom, decorative cushions, candles, lamps, lights, photo frames, etc.
Make up, make up brushes, body lotions, perfumes, etc.
Stationery, pretty note pads, revision cards, rubbers, pens, calendar, etc.
Jewellery, earrings, necklace, bracelet.
Hair accessories.
Books
Smellies, body shop lush, etc.
Pyjamas, onesies.
Drinks voucher for starbucks or similar.
Mine is getting a new wardrobe as main present, and one or two other items on these lists. Teenage girls are quite easy to buy for I think, as they are just younger versions of us, with more choice I think!