Hey, I know this response is very late, but I wanted to throw out the idea that maybe your wife has issues with sex because of some type of abuse earlier in life?  That (and stress, hormones, etc) can definitely make a person wall themselves off from a partner.  Low self-esteem, too.  It might be hard to tell if any of these are bothering her, but maybe it's something she could talk to a therapist privately about.

I hope things improved from when you were posting last!