Get her to shoot some long guns first before buying...Got a shotgun? go shoot some skeet. get her used to the idea of recoil. Alot of people assume that women can't handle recoil, when actually the contrary is true. My wife shoots a 7 mm rem mag w/ no fear whatsoever. I'm not saying yours will. See what she can tolerate. if you have friends w/ rifles, try to get them and pull off a few shots. I shot my first deer at age 9 sitting on my dad's lap w/ his 270. I was probably 70lbs soaking wet tops. My suggestion would be a 260, 270, 25-06 (w/ 120 gr.) or 7mm rem mag, or 7mm-08 w/ a 140 gr. BTSP.
You may even consider the new 338 Federal, which is essentially a necked up '06. I shot one last weekend, and loved it. Recoil was suprisingly light. It is not a magnum, so not to be confused w/ the 338 mag.