Can you ask a parent?

Otherwise I would do a combo of maybe an itunes gift card and a little grab bag of personal items (go to a Body Shop or somesuch and ask them what is most popular with teens).

I second itunes gift cards and I'll add B&N too. My nieces loved lip stuff, nail polish and such.. and they were also into fun, cute pajamas at that age too. One year I got them all these mismatched socks from solmates and they LOVED them. They are thick, warm and wash well!

Not sure if she is north or south, but here where it is cooler, infinity scarves are all the rage. My 14 year old asked for one for Christmas and I notice all the girls at school are wearing them.

Mtn: I do not want to ask parents because they are divorced and her mother would not speak to me and my brother is clueless when it comes to gifts.The Bodyshop is a good idea.

Funkyart: Thanks, those mismatched socks are adorable. I never had heard of them before.

daisychain: She is north, I will also look into the infinity scarves.

Keep the ideas coming, thanks

At Thanksgiving I learned about the no tug hair ties that that age is "in to" now. Like the Sephora link below.

A few of those and the iTunes gift card would make you a very cool aunt, if you were my granddaughters' aunt.

Here is a link that might be useful: Hair ties

We got this at work yesterday as recommendations for Toys for Tots for youths ages 10-15.

Action Figures
Art Supplies
Backpacks / Messenger Bags
Books
Clock Radios
Cosmetics
Craft Kits
Curling Irons / Flat Irons
Flash Drives
Hair Dryers
Headphones / Earbuds
Bike / Sports Helmets
Jewelry / Jewelry kits / Organizers
Legos / Building Toys
MP3 Players
Purses
Radio Control Vehicles
Room Decorations
School Organizers
Skateboards
Sporting Equipment (bats, baseballs, gloves, footballs, soccer balls, basketballs, etc)
Wallets
Watches

My DD is that age. She loves Bath & Body Works stuff -- a gift card might be nice if she has a store nearby. Or The Body Shop, or what's that other store...Lush?

She likes fun patterned socks. She also loves anything "fuzzy" -- socks, fleece tops or pj's, throw blankets. She wears flannel pj pants around the house a lot.

Abercrombie Kids is a new favorite of hers. She likes a lot of their sweatshirts/hoodies.

If your niece likes arts and crafts at all, she might like a collection of fancy duct tape (if you're not aware of the new designs in duct tape, you may be surprised!) or washi tape. Or Sculpey modeling clay.

My DD and many of her friends love Vera Bradley stuff, too. She even has a VB quilt on her bed and on her Xmas list she has a VB throw blanket, slippers, and robe!

I think a lot of girls are getting into jewelry at this age, too. Mine is just starting to wear necklaces once in a while, and she has pierced ears so she wears earrings every day. She still likes small stud earrings, though I did recently buy her a pair of small hoops that she was thrilled with.

I have nieces about the same age. Funky color nail polish, infinity scarves, anything One Direction, cake pop maker, fun socks (love the ones posted!), smallish cross body bag (so many schools no longer allow backpacks but they do allow the girls to carry purses), Old Navy clothing, cute slippers, jewelry.

If she's sporty the Sweatyband hair bands are great. My daughter loves her new Reebok running headband. (Not just for running!) she also just ordered some clothes and an Infinity scarf from Aeropostale the whole store was on clearance & she found some really cute stuff! Good luck!

Schools don't allow backpacks? I really hope it's not for the reasons I'm imagining, but maybe that is the world many live in. Sorry for the hijack, but that statement just jumped out at me.

Maddielee:
Funny you should mention those hair ties, I got some for my adult daughter (30) last christmas after reading all the hype on them and she told me yesterday that they really did not hold. But thanks for the suggestion anyways.

Gssciencechick: That is quite a list, Thank-you.

Sueb: Many good suggestions.Thankyou.

Kimberley:
I like those ideas but never have heard of One diredtion.

Kitchentime: No , she is not sporty at all.

My DD's closet at home is a virtual Vera Bradley graveyard, I think she had stuff in about six patterns. She was the VB overnight bag Queen! Thanks for a trip down tween girl memory lane AND reminding me to take them all to Goodwill! Enjoy your daughters and nieces... It is a wonder and delght when they grow up into young women and are suddenly your friends :-)