To be honest I would avoid the clamshells alltogther They are lovely computers but the screen size of 800 by 600 resolutions have problems displaying most web pages. The are great for collectors, but pratical use is some what limited. The most up-to-date version of the operating system they would install is Mac OS X 10.3 for the iBook models without FireWire and Mac OS X 10.4 Tiger for the model with FireWire.
(Bare in mind that the newsiest Operating System made by Apple is Mac OS X 10.8, which it doesn't support)
The best iBook to buy is the later G4, either 12" or 14" screen. They can be upgraded or even brought with Mac OS X 10.5 Leopard which has a lot more application support available,
But I must add, They are 9 or more years old and will not cope with modem versions of Flash or Java. Limiting them on web sites like YouTube. If she really wants an iBook, then G4 for would be the best value for your money.
Be selective on what you buy and buy something that is working and has the system restore disks.
Hope this helps.
If you want an iBook go with the G4 model. I have one and I use it frequently mainly online (Browsing, newspapers, forums, etc). I also have a functioning Clamshell and it is good to play with occasionally but is a pain to use especially online.
I purchased my iBook G4 from this online dealer which I have dealt with for the past 10years.