Both

I agree with the sentiment to call and talk to a manager.

It may be a brick, but it's an exceptionally capable brick and well worth carrying. At 71, I certainly would enjoy lighter, but the results I get keep me happy with my D500. This does not mean I don't recognize the quality that can be had with lighter systems, just saying one can be happy with a brick.

I keep the Nikon FX 24-120 F4G on my Nikon DX D500. It sits with a Nikon SB400 Flash mounted all the time for indoor grab shots. Outdoors I mostly take the flash off. The Nikon DX 16-80 2.8-4E sits in my bag.

I keep the Nikon 24-120 on my D500 all the time. When I'm indoors I keep the Nikon SB400 flash on it as well. Granted 36mm on the wide end can be constraining but the quality of that lens on a DX body makes it worth it.

Nikon 24-120 on my D500

It's a 1950, in 1953 and 54 Chevys had a more boxy style. I own a 1954.
Rick

I have the D500 and use it in my DayCare business as well as for family and nature. I have found it to be a great camera. It is heavy, but the design fits my hands perfectly and I really don't notice it. Many of my pictures are indoors of young children in action and I have added a SB400 flash which I keep on it when I'm indoors. Combined with the Nikon 24-120 4G which is the lens I keep on it almost all the time and the SB400 flash it yields perfect results. The camera is also quite capable in video mode and the tilt screen comes in very handy. (The 24-120 is equivalent to 36-180 so is a bit limiting on the wide end, but the results have made it worthwhile to adapt too.)
Rick

I use the Nikon 24-120 on my D500 and find it to be an exceptional lens both indoors and outside. It is on the heavy side, but the results I get make it well worth carrying. My wife and I operate a DayCare, so most of my work, both indoors and out, involves catching the children at the right moment. Using the FX lens on a DX body really showcases the best of the lens and consequently the children. I do also have the Nikon 16-80 2.8/4, but it just sits in my bag. The Tamron 70-300 supplements for grandkid's sports although in most cases the 24-120 would be quite adequate. All my landscapes are done with the 24-120.
Rick

Having owned the very fine Nikon 24-120 4.0, that would be my recommendation.

https://photographylife.com/reviews/nikon-24-120mm-f4g-vr

The 5 Mark 3 would be fine (Full frame sensors are great). It provides all the exposure modes she would need to learn the camera and is really the same as learning any of the more advanced DSLR's would be. Biggest drawback I see is the lack of a built in flash, which may or may not be important to her. It's also quite hefty especially when paired with a zoom lens. It would be well to be able to hold the camera and perhaps an 80D for a comparison to see how she likes the feel and heft of each.
RickSr

Nikon has the D750 on sale right now, it's a wonderful camera and a joy to use! Absolutely professional quality.

Sounds good to me, a conscientious owner and a camera that's just getting started at that shutter count for a price you're happy with.

The 80D has an articulating touch screen which I have found quite valuable in taking photos of my grand children. The touch screen is also a big bonus when taking videos of their various events. My choice between the Canon 80D and the Nikon D7200 really came down to the articulated touch screen and as I use it, it really has become quite invaluable. I would also recommend the 15-85 lens, it is quite a bit sharper than the 18-135 that I started out with.

I would agree with that, word for word.