I found all my Kobos nice and simple to use. I actually prefer the Kobo interface to the Kindle. The advantage of the Kobo is that it always shows the book you're currently reading - unlike the Kindle, which will boot your current book off the home screen if you buy more books.
There's a link to your library, and links to the last several books you read, on the home screen. Controls are also easier than Kindle: on the home screen, there are icons at the top for the light, wifi, battery, and Other Stuff. Touch the light icon, and you get the brightness slider. If you want to adjust the settings (or go back to the home page) when you're reading, just touch the middle of the screen (or the middle-bottom - you can change it in settings) and the top and bottom strips with the controls come up. Turning pages is by swipe, and there are different ways you can set it up.
The only button my Kobos have is the on-off button; it's likely the same on the Aura Edition 2.
The only thing is that when you use the search button, it defaults to searching the Kobo Store, but if you just want to search your device (or your current book), you just have to swap it over with the drop-down list.
Honestly, there's not much you can do wrong with a Kobo - and if you (or your wife) have particular reading tastes when it comes to font, font size, and spacing, the Kobo is your friend. It's much more flexible than the Kindle.
Honestly, the Kobos are very nice pieces of kit (which is why I still have two of them), and the Kobo store isn't bad - not as good as Amazon, but at least it exists (unlike the Nook store in the UK, which vanished a few years ago). I'd certainly recommend shelling out the extra £25 for a Kobo; there's a lot to be said for going with a make that at least has a UK bookstore if your wife wants to buy her own books directly on the device.