Having recently changed from a Dell to a Macbook, I can highly recommend the Mac. To be honest, most of the day to day things are the same. I've had it less than a month and already I'm playing around with photo and video editing - would this be something your dd might like?
Also, Apple offers free group classes, so if this is something that she would go to, it might be the perfect opportunity for her to learn through play, if you want. See here (click on workshops) for free options. I see there is also the option of "youth programmes", but I don't know anything about it.
I asked dh his opinion (he is somewhat of a geek!), and this is his answer:
While there are many cheaper PC's, you get what you pay for - a similar quality pc with comparable features will cost almost as much. Also, after dw broke the power connector on 3 laptops in a row, we're willing to pay extra for design features such as magnectic pull-away power cables, etc.
As for compatibility, there are good alternatives to the Windows software out there. For most uses the mac is as good or better than Windows.
Macs nowadays are basically PC's from a hardware point of view. You can install Microsoft Windows on the laptop and run it directly, or you can run in concurrently with Mac OS X via virtualization software, such as Parallels or VMWare, if there are Windows software that you just have to use.