Can anyone recommend a book as a guide to explore Rome's fountains and fountains in the surrounding area for my mom? Beautiful pictures are a plus! Thanks in advance.

For beautiful pictures, you would probably have to buy a book of photographs that will weigh in at several pounds and thus not lend itself to use as a guidebook.

Almost any guidebook to Rome will list most of the fountains; several series of guidebooks are heavily illustrated.

My own Access Rome lists most of the fountains; some are shown in line drawings.

If you only want information, borrow Eleanor Clarke's "Rome and a Villa" from the library and photocopy the pages of the chapter "Fountains" on which she lists and describes the fountains.

Fountains in the surrounding area are generally treated in the "day trip" section of Rome guidebooks, e.g., the Villa d'Este at Tivoli.

amazon.com has a book called
Fountains of Rome, by Venturi

Yes, and it weighs in at 3.2 pounds, according to Amazon.com.

Thanks for the tips! Have you guys used either of these books before?

Second Eleanor Clark's Rome And A Villa, both for the essay on fountains and others on the Campidoglio, Roman churches, palazzi, Hadrian's Villa etc.
The book has been reissued in paperback many times since it's publication in 1952 - get a copy if art and architecture and the Roman "streetscape" are of real interest to you. She's a wonderful writer with incredible knowledge and interesting opinions.