Downtown Disney offers some cool things for teens - Disney Quest & shopping - the Virgin Megastore, movie theater & if think she is mature enough, you could take her to Pleasure Island. She can go in most of the Clubs with you.
My teenage boy usually likes to stay in the Parks til close tho, this is the first trip he's really planning to do any time at DTD / DQ / PI. He's 16.5 yo.