I have three things to say:
1. Does she masturbate? She may have conditioned her vagina to feel sensations that no penis can match. I no longer masturbate after I realized that penises felt boring, and I LOVE sex and was not willing to compromise that!
2. Can she flex her kegel muscles at will? This ability can help her to inprove her sensations, and also get longer and better orgasms. They also can give her more control over her body, so she can help in the "search for sensation." Might I add that you are being very diligent and good to her to put all this effort in, seeing as it's my opinion that women's genitals are more difficult to navigate than a coral reef in a hurricane so it's up to the woman to make sure her man hits home!
3. I've seen vibrators which fit over a man's penis to touch her clit with each thrust. If all else fails, go the mechanical route
