I was technically a teenager about 5 months ago, and trust me, even if we think we don't need help, we do. It is quite easy to just be the kind uncle who dose magic and instantly dose whatever she wants, but it takes guts to take the unpopular stance and tell her what she needs to hear to get ahead. You're not her friend you're her uncle, you can be a friendly uncle of course, but to effectively help her she has to listen, and if you've offered your time to help her, then she shouldn't waste it by sitting around watching TV. I wish I was more strict with my niece.
Bravo!