Joined this forum specifically to reply to this post:
Honestly your wife sounds asexual. I can say this because I myself am an asexual recently in a polyamorous relationship. How it works for us it my two partners (who are pretty damn sexual) handle that part of their relationship, and we share the rest of it.
An asexual is defined as a person who does not experience sexual attraction. That doesn't mean we don't experience emotional or necessarily physical attraction, just that sex is optional rather than required. It usually means we have no sex drive, and in the case we have one (some of us do) it ends at masturbation. There is no desire to involve another person. That's not to say an asexual can't have sex; I very well could if I could work up enough interest...it's just so much work to do so it feels like a chore. Haha.
Of course she could just be hyposexual or any other variety of things, but asexuality is an option (and there are more of us than you think
I recommend asexuality.org if you're interested.