Both those cartridges can be easy on the shoulder, but fit of the gun to the shooter is most important.

Find a gun that fits your wife's frame very well (length of pull, etc.) and then have her try shooting examples of these well fitting guns in the cartridges you feel she can tolerate.

Fit of the gun to the shooter should be foremost.

BUT, I'll toss in that the .243 can be very forgiving in terms of recoil. I have one and can spend hours at the range with no appeciable effects except I'll gain a boatload of empty brass.
I've never shot a 7mm/08 but have heard many say it's quite forgiving also.