There are a lot of factors........shoulder width is much more critical than height as to length of pull, experience with rifles is another factor. Length of neck is also very critical for eye relief as women generally have longer less muscular necks than men. So to keep with the general train of advice here, it is important for her to try as many as possible in the store to see what goes best with her physique. Caliber is much less important, I know several relatively small ladies who shoot .375 H&Hs like they were 22s. This comes with conditioning and familiarity with rifles, shooting and recoil. As to caliber/cartridge.........I have always said the .270 Win is a perfect ladies cartridge, so there is no point in changing my "party line" now. Anything in that range of cartridges should be well within even new shooters abilities to master.........7-08, 25-06, 257 Bob, 260 Rem, 6.5X55 or 7X57 in a modern rifle or even the 257 Bee and 264 WM are pretty easy to shoot and extend you useful range significantly.