Amazon Kindle 16 GB (newest model) - Lightest and most compact Kindle, now with faster page turns, and higher contrast ratio, for an enhanced reading experience - Black

Colorsoft - $160, Waterproof, 7" diagonal screen, color. Paperwhite - $125, Waterproof, 7" diagonal screen, black and white. Basic - $85, not waterproof, 6" diagonal screen, black and white. To preface, ALL THREE are going to be wonderful reading devices. They are all different and will have their own pros and cons, but none of them will be a bad choice. I personally prefer the colorsoft. Having color book covers (and images where available) is a delight, feels more premium, and has helped me connect more with what I'm reading. The 7" screen (also on the Paperwhite) gives VERY noticeable additional space on every page, which means less page turns and the ability to make the text larger (if your eyes need it) without dropping to 10 words per page =P. Being waterproof means I can ready the pool or at the beach (or in the bath ;) ) without worrying about killing it. Some people prefer the Paperwhite as it is has a slightly more contrast. I have both and I don't believe the difference is significant (think 3-5%, not 50% lol). I have a colorsoft and never once have I thought "man, I wish I were on my Paperwhite so it would be 3% darker" lol. And more importantly, you'd never even know if you weren't sitting there comparing both side-by-side. I got my wife a Colorsoft and she has not once ever said anything about the screen other than it's beautiful. And there are lots of people that prefer the basic model, not because of the price (well, not JUST because of the price ;)) but because it's smaller, making it easier to tuck into a purse. It's not waterproof, which may not be an issue for your wife, but it also has an inset screen, which means dust/lint/sand can get stuck between the screen and the bezel. If you think she'll be reading in adverse environments I'd choose either of the waterproof kindles with a flush screen. As for the "signature editions" -- I don't really think they're worth it. They add: wireless charging (QI compatible, not MagSafe, meaning it doesn't auto-align), an ambient light sensor, a "tap" sensor that lets you double tap the back (or anywhere) to turn pages, and usually double the storage space. I know those sound like nice features, but I don't use any of them on my Paperwhite SE. The battery lasts forever (I charge once a month) so wireless charging isn't as important as say on a cell phone, the light sensor changes the brightness for you but isn't perfect so you end up changing it manually anyway, the tap sensor gets false positives and/or doesn't pick up intended page turns, so I turned that off, and the storage space is moot since most people's entire libraries are a fraction of the basic size (and stored in the cloud anyway). Final thoughts: you can't go wrong with the paperwhite. It's the gold standard. But if you want to go above-and-beyond, give the colorsoft.

the firmware says 5.19.4.0.1, model is https://www.amazon.com/dp/B0CNV9F72P?ref=ppx_yo2ov_dt_b_fed_asin_title