My mom is the very definition of computer illiterate -- my sister and I have been trying to teach her to use a computer (first a PC, later a Mac) since the mid '90s, and she simply cannot grasp the basic concepts. She can sort of work a keyboard (it looks like a typewriter), but mice constantly thwart her. Add to that the fact that she has trouble discerning "windows" on a desktop as being discrete items, and you can see why we finally gave up trying to teach her once we had both gone away to college.
About a year ago I managed to acquire an unneeded iPad, and made the decision to gift it to my mother. For a woman who has literally never used a computer without assistance, never mind owned one, she took to it immediately. She's now able to browse the internet, send and receive emails, and even navigate the app store when she wants additional functionality. And after a full year, I haven't received a single "oh no, I think I broke it" call.
That being said, my mother is not your mother (AFAIK), so your mileage may vary. If you think her needs can be satisfied by an iPad (web browsing, shopping, email, media consumption, and no more than light content editing), I highly recommend it. There's just no beating its ease of use. An external bluetooth keyboard would be nice for longer writing sessions, however.