Is she interested in Science and Engineering?
If so, the free NASA app is a wonderful resource - explore the Universe, see the stars, watch NASA TV and see the astronauts on the International Space Station *Live*.
Plus they have all the Apollo moon landing videos there too...
Don't suggest games - there are so many more exciting and interesting things to do..
If she's into Maths, then the Wolfram apps - OK they're not free - are truly amazing.
Is she a budding programmer? Or iPad app developer? Then..
If she feels like learning how to develop her own apps she can do so for free. Go to iTunes on your iPad, click on 'iTunesU' at the bottom right hand side, select 'Universities and Colleges', then scroll to Stanford. Scroll right through the courses and you'll find a 25 lecture course on programming iPad apps. It's free and, by the end of the course, you'll be able to program some simple apps yourself. It's a great resource from one of the best Universities in the world.
And it's not difficult - she could be the next Steve Jobs...
We need to encourage the youngsters of today - the future is in their hands - and it's an incredibly exciting world to grow up in. The US lead the world in the 20th century and I was incredibly inspired by the Moon Landing program - it's what made me become a scientist - we need to encourage the next generation of scientists and engineers that will drive the economy during this century.
Tim