Hi RR
Here's an idea. I've got an iPhone 4S and have NavFree on it. Its free satnav software. Download from the App Store. It works very well indeed - I used the US version on honeymoon last year and the Canadian mapping is spot on in Vancouver. It works great in UK. Its not as beautiful or graphically perfect as TomTom or Garmin but its...Free! See how your daughter gets on with a phone based Nav system first; if she likes it she'll definitely like the paid-for versions. Remember, all the Nav data is basically the same, just different graphics and menu's.
Hope you find the right one.
PR