Been moose hunting, never shot one. I took a Remington 7mm Mag with 175gr partitions. I lived in Alaska and had several taken by friends and family.
Moose 1: 458 Win Mag 500gr bullet taken by high school girlfiend's dad. Not recommended.
Moose 2: 375H&H with 300gr partition taken by my Dad. 5'7" and 170lbs. Not recommended.
Moose 3:338 Win Mag(very pop. in Alaska) taken by friend of Dad, Jake. Not recommended.
Moose 4: 308 Win taken by coworker of my dad's. Recommended.
I would stay away from magnum anything unless there is massive recoil brake, heavy rifle, and 2-3 dead mules in the stock. Wouldn't be fun for her to carry such a beast.
Moose are pretty docile, except when they are pissed because you almost run them over with your snowmobile. We had them in our yard in Anchorage. Of course, the bastards disappear come hunting season.
338-06 and 405 Win are pretty popular guns with soft recoil compared to bullet weight. A semi-auto might help, like a BAR in 270Win or 308 Win.
The hunting we did for moose was pretty much less than 150 yards. Everyone recommended shooting one next to the river.