City miles are basically severe duty, IME. Still makes it too early mileage wise, but not that early age wise. But if the fluid is a healthy color, has that new fluid smell, and is at the correct fill level, probably doesn't need to be exchanged. Def make sure no leaks are present. If your Edge is AWD, I'd be more concerned with the PTU.
I'd get a second opinion from a reputable service shop (you can find them via Yelp, Repairpal, etc., and actually look at the reviews).