@RedMaple Hi, in regards to your wondering if a woman can use a men's sleeping bag, I'd say yes. I'm getting the men's short (I'm female). As long as the length and width are appropriate, there's not much need for difference in men's and women's sleeping bags. I'm not an expert, though. This is just my opinion.
Meliabedelia@meliabedelia is spot on - the interior volume of a sleeping bag is critical to warmth retention. If the length and width are close to what you'd buy anyways, @RedMaple, then you should feel confident in getting this bag for your wife. The Mens Short fits up to 5'6" and the Womens Regular fits up to 5'8". While the Womens Regular is actually longer, it actually has 2 more ounces of down fill. So, it seems that the two bags would be pretty similarly rated, with maybe a slight advantage in the Womens Regular. Hope this helps!