No.

Flat and simple.

You can check hormonal levels and any psychological issues, but the fact is that women are extremely complex and I've come to believe it really has to come from their side. You can make a romantic dinner with candles and a romantic movie and it will be perceived as putting pressure on her. You can open doors, walk with her so you're on the street side for her protection, all the chivalrous things are just thanked. You can do foot rubs, but she doesn't like you touching her "gross" feet. You can compliment her and she won't take the compliment.

You can try strawberries and chocolate, Estroven, female HGH, soy, hanging upside down with bats. Anything that works will be specific to her and her only.

So first it has to become an issue to her. As long as she is happy with the relationship, then nothing will change. Then she has to figure out how she can increase her libido ... you can help, but it's up to her.