having taken moose with cartridges ranging from 6.5cm and 6.5x55 to 9.3x62, in magnum and non-magnum cartridges over the past 37 years, i can attest that they all work to put meat on the table when the bullet is placed properly. And my longest shot to date has been 220 yards (7mm stw) , with the shortest at 15 yards (6.5cm). (my archery kills have all been been inside 40 yards).
the big thing for the op is finding the rifle that will fit his wife properly and be within her recoil tolerance levels to ensure comfort, confidence and competence. many goof rifles out there that will make the grade for her. Do not go too light, as weight helps with felt recoil. a good recoil pad makes a huge difference, if the factory apd doesn't cut it. Tikka's pads are usually pretty stiff, whereas the browning pads are softer.
Had to replace the factory pad on my wife's steyr mountain classic in 7mm-08 with a limbsaver to make it more comfortable for her. 140 gr ammo is where she is comfortable, whether off the bench or shooting sticks (her recoil tolerance limit). She much prefers to shoot her 250 savage, but will be her deer rifle (her choice).
The other question would be which moose will she be hunting? Alaska/yukon, canadian or shiras. Big difference in body size between the larger and smaller species that may warrant her wanting a little more performance to ensure adequate penetration on less than desirable shot angles, and/or limiting shot distance.
Thankfully, most women are more patient than men and will wait for the right shot presentation, and will usually pass on uncomfortable shots (for them), whether it be distance, presentation, or stability in shooting position, and therefore make better shots.