Take Grandmom to the store and let her choose the one that she likes. Model is of far less importance than one that "works" for her.
YEAH....tirediron is right: in another life, I used to sell cameras at retail, at a well-stocked store with lots of models, from all the big names. My experience was that women tended to prefer smaller, lighter models than men did, for who knows, exactly, what reasons. I NEVER sold an F4 to a woman...they loved the many smaller, lighter, more-nimble-feeling models.
D7100 for sure. You can't see out the viewfinder of some smaller cameras, the viewfinders are too small. D7100 had a good viewfinder.
Possibly a used d610 if that fits in the price range... probably won't though
On these suggestions: used D610? YES. Great image quality, period. Uses FX-type lenses, can shot DX lenses as well. Decent viewfinder. Built on the D7000 chassis and substems originally as the D600; different, tougher, better shutter as the D610 incarnation, so it is smaller than a D700, feels lighter too. D7100: best 24mp camera at its price range. Sensor is very good except slight banding on wayyyyyyy under-exposed and then lifted shadows, otherwise not much to worry about. Viewfinder image magnification on the smaller Nikon 3xxx and 5xxx cameras has been ticking upward every generation; compare a D3100 vs a D3400, it's better, but still the 3xxx and 5xxx are penta-mirror cams; the others have all-glass penta
prism, so a better thru-the-viewfinder image. Used D600 bodies sell for less than 610; as I understand it, you can get a 600 replaced by Nikon with a 610 by complaining about it, based on Nikon's guidelines. Sort of a
make-good-concesssion Nikon made to its loyal customers.
As far as "what works" though, for your wife; the 5xxx Nikons have the flippy screen.Some people reallllly like the flippy screen! The Sony A6xxx models have the rear LCD as viewfinder. A LOT of people are happy with, or like, or love, framing up their photos on a BIG, 3" or 3.2: rear LCD type screen. In some ways, I think that might lad to better photos, esp. for the novice/intermediate"--by looking at a BIG, flat, 2-D image on a high-grade modern LCD screen...this metaphor for hoew to frame up a picture has some strong merit. I think it might actually lead to better composition than say, squintimng through a peephole finder on a Leica M3.