Okay, first of all, sorry to respond so late. I didn't get any email notifications so I figured there were no new posts. Second, sorry to rekindle an old argument about composition with respect to painting vs photography. Though it makes for interesting reading.
Isaac and RSL, well played in getting back to the subject: my mom and her desire to improve the composition in her photos. Aside from shots of her dog doing goofy things, she has always loved shooting nature. That can mean flowers in her garden, birds in her local park, or scenery and landscapes she can encounter in Asheville, NC (including the Biltmore Estate). She's in good enough shape that she can walk for a few miles, though any climbing is pretty much out of the picture.
She loves photography, and has a passing understanding of exposure. Her biggest problem is that she needs to be able to do a better job of taking what she sees in other photographers' work, and incorporating it in hers. I don't want her to just copy other photographers, but she could do a lot worse than imitating great photos while she develops her own style. I think a book illustrating such basics as balance, rule of thirds, foreground vs background elements, lines, etc. would be very helpful.
Hope this helps to understand the type of book I'm trying to find for my mom. In the meantime, I'll check out the books already mentioned.