She might want some basic grooming tools. They don't have to be fancy - a hoofpick (I like the kind with a brush, but I also have the kind that's plain metal to stick in my pocket when I trail ride, in case of emergencies), a body brush, a soft brush, a rubber currycomb, that should be enough. The Oster tools are nice because they're more ergonomically design, but they're also about three times as expensive. Horsemen have been using the traditional tools for centuries, pretty much (I looked through a reprint of a tack catalog from the late 19th century once - it's amazing how little has changed).
Beyond that, it depends. Is she riding Western, English, or both? If she's not a very experienced rider, I suggest starting in English, if possible - much better for your balance. I started in Western and switched to English, and even though I like English better, if I haven't ridden in a while I'll do Western, because I know my balance will be terrible otherwise. I ride in jeans and a pair of basic cowboy boots - don't bother getting the super-fancy ones with rhinestones and pink leather and all that junk. My jeans and boots work for both Western and English, although when I get to the point where I can ride on a regular basis and I'm riding English more, I'm going to buy some breeches and boots. Beginning equipment doesn't have to be fancy - remember, a lot of girls her age will like horses for a while, until they discover there are far more fascinating creatures, boys. Not that this will necessarily happen (my mom thought it would with me, and fourteen years later, I'm about to graduate with a degree in Animal Science because I still like horses!), but it does happen quite a lot.
If I can help you out anymore, PM me. I'll send you my phone number and I can talk to you about it if you'd like.