Hi IvorW, The iPhone is an obvious choice here. There are many tweaks that can be made to integrate nicely with her current email address. For painlessness-sake, this would be choice 1.
The TREOs from Palm have their own version of calendar if my memory serves me well, so would not be exactly spot on. Yet it could be possible. When it comes to integration with iCal, it can be quite tricky but with the use of spanningsync, you could use any phone that can work with google apps(a fine choice for small businesses) Hope this helps, Livio