again, unless she is going to carry this gun, you are thinking all wrong. the shorter the barrel and the lighter the gun is, the harder it is going to be for her to shoot it because the recoil has to go somewhere, and she is going to absorb it now. a heavier gun recoils less than a light one in a given caliber all other things being equal.
i am guessing by your post that the weight while holding it is a concern; it shouldnt be. if she is that weak that she cant hold up a gun because of and extra 2" of barrel, you have bigger concerns than potential threats to you while camping. i am not trying to be a smart aleck, just telling it how it is. again, if you are intending to carry it all day, different story. but if it is a "nightstand gun" you are way further ahead with the 4 inch barrel.