Since I don't have mod points, I'll second (and add to) this comment.
My scenario was almost identical - elderly parent, not tech savvy. I got a Kindle Fire HD five months ago, and have had no tech support calls. I added the most common apps to favorites (like Skype, E-mail, Browser), and configured them (disabled in-app purchasing, added e-mail accounts), and handed it over.
The carousel is one of the best features for this use case - my dad doesn't want to pin 20 widgets to the home screen; the carousel easily allows him to browse the most recent apps (the four or five he uses) and books and videos without having to shift home screens, navigate to an app drawer, or any of that. In fact, he might have forgotten all about the favorites since everything he needs is on the home screen (well, except the prime videos, and he discovered that on his own).
While it wasn't on the Fire HD, the new mayday functionality might be useful as well. And the audio and screen are really good (especially the audio - better than all my other tablets, and even my laptop speakers). He likes the swype feature - a huge drawback to the iOS devices (apart from the complexity - seriously, until you see how simple the Fire is, you won't understand how much the multiple home screen nonsense, hidden settings, etc. obfuscate a system for someone who doesn't want to learn about tech).
The drawbacks are the google apps are missing - especially Youtube. You can root it easily enough, but I'd recommend not going overboard - make underlying system changes, but don't change the UI. I feel the carousel is best for the usage scenario you have in mind. KISS principle.