Personally, I am always a WM-fan.. There is just so much that a user can grow up with, that you start to realize the device's true potential. I have no clue what Instinct is running off of, but it seems that it just is a glorified GPS/Phone with some multi-media features. Still, I never knew all of the stuff that my 6700 could do when I got it at first, but after 4+ years almost with WM, I am soo glad I didn't go for convenience or simplicity. Don't get me wrong, WM is pretty simple and WM6.1 handles Mobile Email very very well.. I'd just get her the Diamond Pro, and get a good backup program, Spb Backup for example, and have her use this:
http://www.scheduleworld.com/ to backup her contacts and notes/tasks/calendar, so it is always up-to-date. Both Spb Backup and the sync-client I mentioned above can be setup to be automatic. So, maybe that is something you'd find helpful.
Andrew,