That's the way that the Love Goddess, a woman sex therapist who ran the Erotic Highway board here a few years ago, explained it.  The woman's hormone levels decrease to the point that she had little or no sexual desire.  The Love Goddess recommended bio-identical hormone replacement, which she said was a way of replacing the hormones without the side effects that synthetic homones pose.

http://health.msn.com/health-topics/sexual-health/womens-sexual-health/articlepage.aspx?cp-documentid=100186622

A woman's desire for sex is based on a complex interaction of many components affecting intimacy, including physical well-being, emotional well-being, experiences, beliefs, lifestyle and current relationship.

http://www.letlifein.com/articles/sex-what-women-over-50-crave-more-than-orgasm/

What [most] women crave more than the orgasm is love and intimacy. That’s very difficult for [most] men to understand.


While it may be something medical, you haven't suggested that it is. More likely (again, for most women) it's the emotional component that's missing. I don't know your situation, so this is just a general observation. Like most songs that stand the test of time, the lyrics can be applied in different ways:

The Who - Go the Mirror!   http://www.youtube.com/watch?v=wPzY30v9mtg

What if she's thinking this:

   He seems to be completely unreceptive
   The tests I gave him showed no sense at all
   His eyes react to light, the dials detect it
   He hears but cannot answer to your call

   See me, feel me, touch me, heal me
   See me, feel me, touch me, heal me ...

Then this would be good advice:

   Go to the mirror boy
   Go to the mirror boy ...

I know lots of women who've gone through menopause and still love to fuck. Bodies change, but sex doesn't have to. Have you tried spicing it up with toys, sexy games, videos, fuzzy handcuffs, flavored lubes? Get thee to the Smitten Kitten, friend.

(Also, I know this sounds crazy, but maybe you could, like, have a conversation with her about it?)