I'm not sure of the stature of your wife. Why don't you take her to the gunshop and let her try a youth stocked rifle? It may fit her better than the longer one. Heck I even have a couple youth rifles thaty fit me so good and I'm 5'9".
As for cartridge - anything from .243 up will do nicely for deer. Some youth models to consider are from Savage, Browning, Remington. I got my Grandson a Savage 11FYCAK (or something like that) in 7-08 with detachable box mag., and adjustable muzzlebrake. That little rifle shoots 1/2" groups using Hornady 139 gr bullets.