I think she really needs to talk to you, and possibly a professional (physical or mental, or both), but if she won't talk to you, you have to choose if you want to stay with her with this hanging over you, or if you would be better off moving on.

Many women don't consider a low or no sex drive a problem. I don't know why--I consider it a problem--but I have heard this on talk shows and read it in magazines where they polled women. I think it comes from the way women are taught about sex and how they feel about it, vs. how men learn and feel about it.

It's not unusual for members of a couple to have differing sex drives. If one wants it more, and the other wants it less, they have to try to come to a compromise, or one has to give up or give in (which can lead to resentment), or break up.

As for being a nympho, I doubt it. While people use it to refer to women who want too much sex, there is no actual definition of what is "too much." Having a high sex drive is only a problem if it causes problems for you, such as neglecting things you should have as a higher priority (such as family, work, relationships) in preference of having sex, putting yourself in danger (having unprotected sex or sleeping with lots of strangers), or something like that.

I don't think there's anything wrong with putting an emphasis on sex, if it's important to you.