What about an offer to donate $X to a non-profit of her choosing?
My “counter-culture” kid’s favorite present every time is a gift certificate to a local used clothing store or thrift shop. If there aren’t any in your niece’s town, I like the idea of an alternative bookstore.
Maybe I was just a dysfunctional alternative teen, but if one of my “old” relatives gave me a Krazy Kat collection when I was 14, I probably would never have cracked the spine and would have been reluctant to explore that strip’s genius as an adult.
Gift card. This isn’t hard. If you’re nice, it’s one of those you can get cash from.
The Hallmark card can be personalized for her identity. But just give her $. She doesn’t have a job! (Assuming)
Terry Pratchett books, especially the ones with Magrat Garlick.
Or a consignment shop, but whatever’s it’s called it should be known for its selection of things people actually want to buy.
Getting the older sister to help you spy would not be a bad idea. Your niece sounds a lot like my daughter, and it could really help to know if she has that particular My Chemical Romance T-shirt you’ve been eyeing at Hot Topic in her closet already before you buy her another one.
Seriously, if her sister can tell you what anime she’s into, there are all sorts of things from messenger bags to T-shirts to specific cosplay items (“But I’m not Misato Katsuragi! I’m a red blood cell from Cells at Work!”) that you could pick up.
Copic markers … man, there’s a dark hole. If I could get a refund on the retail value of all the Copics in my cabinet, I could buy myself a drawing tablet instead!
Guess I’m just old-fashioned …
I wonder if she’d enjoy browsing a vintage toy shop.