I actually just read this today as I am considering a muzzle up shoulder rig for my S&W
Shoulder Holsters: Beyond The Mystique
from the article:
Its a good read but a little lengthy, I just copy and pasted the part about Women.The Lady's Option
The last but perhaps most frequent candidate for the shoulder holster is the female pistol-packer. If you hang out with plainclothes units who have the shoulder holster option, you'll notice that a large number of the female officers will wear that style. It saves them from having to wear mannish pants with loops large enough for the sturdy belt needed to carry gun, spare ammo and cuffs. The self-suspending nature of the shoulder holster makes it work very well under a woman's suitcoat, blazer or sweater.
Hip holsters designed for men tend to ride too high on women. While most men have trouble reaching across their chest to get a good grip on a shoulder-holstered gun, the women find their relatively more limber arms can reach much farther toward their opposite side armpit.
I wasn't the first to discover this. In his 1960 book, Handgunner's Guide, holster designer and quick-draw expert Chic Gaylord said of his horizontal Dynamite shoulder rig, "This is undoubtedly the fastest shoulder holster made. I designed it originally for policewomen. However, diplomats, heads of state, and our best-dressed detectives went for it to a much greater degree than did their sisters-in-arms."