IWB holsters are pretty much unisex and there isn't much that can be done differently to accomodate women better. It's not a matter of the holster as much as it is the way women's clothes are cut. Women generally where their belt around their waist. Men around their hips. Because women generally (least before a few kids...) taper in to the top, holsters are made with some degree of outward cant to keep the gun more vertical. Of course, that causes concealment problems and apparely restrictions.
Generally though women can wear an IWB either over the appendix area (concealment & comfort problem) again) or well behind the hip (reach problem).
My wife has both types and often yields to a small pocket gun or one of those pocketbooks with a built in holster. I don't like that because the pocketbook is a theft target in its own right and I just don't like the gun being off her body.
In short, your wife is going to have to find out what works for her in terms of utility, comfort, and wardrobe changes.
You might try to find some issues of Women & Guns magazine. They frequently have articles on the subject.