I think a 7-08 or a 270win would work fine. Even a 6.5mm in something at least as fast as a 260 rem are used with success. I know women that shoot them well. I'd put at least a 140 grain pill in either and go from there. They'll both do fine as long as she can place the shot well...and I know what forum you're on but I wouldn't have her doing any long range shots on elk with these.
Some of the 30 cal non-mags will work also, but you do get in to more recoil, generally speaking.
Now, if you're looking to build/get a rifle for her and use it for yourself as well, I'd go 280AI or the 6.5x284 just because they're interesting to me and the brass is being produced now.