Sounds like your sister has most of what she needs, re: drawing software and materials.. Good pencils and paper, are all you really need. And you've already given her the means to begin exploring the digital-end of things..
When I was her age, I found some softcover collections of Frank Frazetta's work; and it completely overwhelmed me! So I would suggest buying her some nice art books featuring some of her favorite artists? You say she's into Animé -type stuff?.. I'd head down to your town/city's best comic-book shop and ask a clerk to hook you up with some of the better Manga collections, etc. If it's anything like the Toronto market, the retail staff will probably already have a very good idea of what's selling and popular!
Non-artists convince themselves that creative people simply "dream up" things with their over-active imaginations.. The truth of it is, if you don't load up the mind continually with exciting inspirational images.. The effects will be felt at the Drawing Table. The wellspring eventually dries up. And "new" ideas will be harder-and-harder to come by..
A nice collection of books should be attainable for about half of your proposed gift budget. And she'll be delighted to finally have artbooks at arm's length, that she can reference to create her own artwork!