I would also recommend counseling, and not just couples counseling for the two of you, but professional psychological counseling for her. It sounds as if, were the sex nominal, that the two of you might be able to have a happy marriage, and her lack of sex drive is not nominal. And if her aversion to sex is because of rape or assault in the past, then she needs psychological help, not just to save the marriage, but in order to live any kind of happy life, regardless of her relationship status. People who have been sexually assaulted have problems that go deeper than just not wanting sex that need to be addressed.
Get her that help and lay off the requests for sex while she's in therapy. Get couples counseling to see what the root of the nonsexual problems might be. You may find that she becomes a happier person and there is hope for the marriage.
[SIGPIC][/SIGPIC]Moderation in all things, including moderation.