Have you looked into hormone levels? Various aphrodisiacs?
Yes, checked hormone levels.
Aphrodisiacs? Sure, a glass of wine, romantic dinner, fun times together. Those are aphrodisiacs for most women, but not my wife. She enjoys it all, but not a hint of sexual interest results.
Other aphrodisiacs? I can't think of anything that doesn't have a very unreliable record, though I'm sure there are anecdotes and certain people who swear it works for them. The FDA recently turned down what might have been the first official "Viagra for women", mostly because it was only marginally effective and had too many side effects.