Yes you could use anything running Windows Mobile 6 should work fine.
You could use any Blackberry phone as well, but you will need to setup a Blackberry server as well if you use a blackberry.
By default only the inbox is synchronized. You have to go in and “manage” the mail folders on the device to synchronize additional sub-folders. On mine I only choose to synchronize some of my subfolders, not all off them. How to do this depends on which device you wind up selecting. It’s possible she can sync sub-folders now, but just does not know how to set that up on the current device.