If she is likly to want maximum portability and connectivity I would suggest Intel Centrino. The P4 will offer more raw power, but is also likely to be heavier, so in my opinion more suitable as a space saving desktop replacement.
I bought a Dell Celeron based (466) notebook some three or so years ago. Mainly on price, but I wish I had opted for a fully fledged P3 as I now find it struggles more so I feel than a "proper" CPU of the same age would. The modern Celerons are of course much faster and much improved too I guess, but I (and this is just my gut feeling) don't think I'd ever buy another Celeron based unit. (laptop or desktop)