I used to love the 25-06, but the .243 has almost identical balistics whith the same weight bullet! (100gr)
Ethical/quick kills being at the top of my caliber choice criteria list, I believe the bigger the animal, bigger the gun.
But the shooter needs to not be scared of the kick either.
The .270 and .308 both puching a 150gr bullet have almost identical recoil (17ft lbs / 17.5ft lbs respectively) (According to the Chuck Hawkes recoil table: http://www.chuckhawks.com/recoil_table.htm )
But the 7mm-08 pushing a 140 gr bullet only has a recoil of 12.6ft lbs. My choice.
I got my son one when he was about 14 or 15 and we took Antelope, mulies, and I even took a cow elk because I was wondering if the gun was big enough to do the job. It did, she went maybe 80 - 100 yards.
Best advice, the more you and she go out and shoot, the more accustomed to the gun (recoil, noise) she gets. That can't be ignored! Shoot more . . . shoot more often.