You sound like you could be my husband! And SpringChickenGoldBrass sums it up in a nutshell when she writes of "the other partner becoming steadily more and more defensive and repulsed." That's me.
So, I don't know whether it might help if I give you a bit of my perspective on the situation, given my apparent similarity to your wife's situation.
I have pretty much zero libido and have felt this way for about 5 years now. I have sex out of a sense of duty and, yes, I'm mightly relieved when it's over. The way I feel at present, I would be more than happy with the prospect of never having sex - with anyone- ever again. My libido really is that low - though that wasn't always the case.
What do I think could possibly help? Perhaps a trip to the GPs to get checked out - it's possible I might have a hormone imbalance. Yet it is hard to motivate myself to go there because I, personally, am not particlarly bothered by my lack of libido. What does bother me is the effect it may turn out to have on my marriage. In other words, I would be seeking possible treatment for myself to make someone else (i.e. dh) feel better, if that makes sense. (To try to better explain, I see this as very different from getting treatment for something like erectile dysfunction where a man has the desire but not the capability.)
Other possibilities I have mused about? A different approach from dh. When he tries to initiate sex, I feel as if I'm being groped. I feel very tense and, yes, repulsed. I think he could take it all a lot more slowly and also allow for more non-sexual touching and cuddling. At the moment, I tense up when he makes any sort of physical approach because that basically means he wants sex. Possibly, if he could say something like "it's ok,I'm not after sex" (and mean it) that might help me relax a bit more. So yes, the people who advise you to back off have probably got a point. I think if you could completely take the pressure off for maybe a few months, that might well help. Of course, there are no guarantees, but I feel it would really help in my situation. I would suggest it is worth considering at least.
Other contributing factors which may or may not be of relevance to you? Dh's behaviour in general. Don't get me wrong, he's a decent man who I care about and who cares about me and the kids in return. But sometimes, I feel as if I have 3 children, not two. As an example, there was a thread yesterday about someon'e dh shtting the bed and then not saying anything and basically leaving his wife to fid and clear up the mess. Well, that wasn't my husband - but that's exactly the sort of thing he would do. If he is in any way unwell, he is inevitably rendered incapable of speaking, moving, getting out of bed or generally doing anything whatsoever. If I am unwell - well, I just have to get on with things as best I can. If dh wants to go out, he goes out. If he wants to slob around all day on Sunday, that's exactly what he does. Basically, the assumption is that I will look after the house, kids, meals etc and he will contribute if and when he feels like it. (OK, I've probably made him sound like an ase. But he isn't actually all that bad. Just a bit childish at times).
His appearance. Ok, he does sport and has a decent body. But I find his propensity for walking around nude anything but erotic. Or worse, he'll walk around with just a t-hirt on with his undercarriage flapping in the wind. His hair is in a "nobbish" style (imo) - but he refuses to change it or even "tweak" it to look a bit more "with it". If I tell him I don't like a shirt or t-shirt, he will keep on wearing it "for a laugh". Don't get me wrong, I don't spend all my time criticising his clothing or appearance - it would be more a case of us going out somewhere and him saying "oh yeah, I'm wearing that orange t-shirt that you hate, ho, ho!". (I wouldn't go out with him deliberately wearing clothes which I knew he hated).
Ok, these are personal things which may have no direct relevance to your situation. But the point is, these are things which annoy or irritate me, which dh knows annoy or irritate me - but which he does nonetheless. I know dh doesn't mean any harm by these things, but I think they are avoidable and unnecessary turm-offs. What I am trying to sday is that there could be some aspects of your behaviour or relationship which would appear to be divorced from the physical side of things but which might nevertheless have an effect.
Look, I don't know whether any of this may have chimed a chord with you. I was just trying to give you any idea as to some of the kind of things that might possibly be an issue on your wife's part. I suspect she would like to talk to you about her lack of libido - try to remember that is is very real, but it isn't anything personal. I strongly believe that my libido-less state is a passing phase and I suspect it will be for your wife, too. Patience and understanding will go a long way I feel - as will trying to show your love and appreciation and working on other aspects of your marriage, not just the obviously physical or sexual aspects.