I have a Sony 900 (7" with wifi) and love it. I had a Sony 600 but gave it to my mother (give a gift, get an upgrade!

), who loves it. I would rather have the touchscreen than the wifi, although it IS nice having both!
I get most of my books from the library, free books from the Sony Reader store, and buy a few from Kobo or Books on Board or the Sony store.
The touchscreen is great for taking notes on the text, or jotting a reminder to myself, or drawing a picture -- and double-tapping a word for the dictionary is priceless! When I read paper books now I forget and try to tap the page to get a definition!
Whatever you get her, don't forget the booklight, case, and screen protector. She will love having so many books in such a small package, especially for reading in bed, no matter which you choose!
Happy gifting!!