OK Lost...I will just play devil's advocate here (and you can tell me to shut the hell up if you want, just realize I am only trying to make you think)....
Did you read my blog today, the post about "talking" open and honestly about sex?
(if not, please go read it now and then come back with an answer)
So after considering what I had said in that post, what is YOUR part in this? When you say that you felt that she seemed to enjoy sex earlier in your marriage, why do you say she "seemed" to enjoy it? Did you never discuss it with her? Were there never words expressed about it?
I am trying to help you get to the bottom of whether or not her statement was true, or whether she said it in an angry moment, or whether she really doesn't know herself if she enjoys sex or not. While it may seem very simple to you whether or not she would know if she likes sex or not, it actually is not that simple.
So back to my question to you....why don't you "know"? Did you never discuss it with her, and if not, why not?