I've fitted a few women up with rifles and shotguns through the years. The article by JDYoung is on the money. It is more than length of pull.
First thing - check dominant eye. If she is left dominant then nothing will make her comfortable behind a big RH rifle.
Then, generally...
Women have longer necks than men.
Women have higher cheekbones than men.
Their jaw tends to be finer (less 'square').
These three add up to the need for a higher comb on any gun.
Women have different chest structure.
The breast tissue starts up at the collar bone and grows thicker as it descends through the normal recoil area.
They have less muscle on the chest.
These mean the recoil pad needs to be angled to suit and is not as square to the bore like it is for men, usually the stock is cast off (outward from the centreline). Sometimes, the toe needs to be angled off a little to allow for larger breasts.
Upper body strength is less. A gun which is heavy out front is going to be a problem for most women to hold effectively. Lighter barrel and shorter forend.
Finally, in addition to shorter arms, women also have smaller hands. This means that the grip needs to be closer to the trigger so they can reach and have control, the grip is usually smaller so a good control is made.
So, take a look at a Weatherby Camilla for inspiration of a designed for women rifle.
The Vanguard Camilla Rifle—“designed by women, built by Weatherby”—incorporates a high comb, along with a number of other features that make this rifle superbly comfortable to shoot. Aptly named after the first lady of Weatherby. FINISH Barrel/Receiver/Trigger Guard - Matte, bead blasted, blued...
weatherby.com
Camilla.
BackCountry.