Oh no! I just typed a long reply to you and accidentally closed the window before it sent!
Here is it again!
First off, has she used an Apple computer before? It can be a big change from Windows, and not everyone is ready to make the step. Don't lay your money down until she's used one.
The 15" PB G4 tops out at 1.67Ghz. There are two 1.67Ghz revisions. The later revision has a better screen and DDR2 RAM, try to go for that if you can afford it. The first 1.67 revison...