There is no version of female viagra, because female libido is even more hormonally complicated than male libido. Additionally, women are WAY more in their heads when it comes to sex, most of us do not compartmentalize sex/life the way men do. I once heard a sex researcher say that you could cut a guys head off and his body would still want sex. With a woman it's almost ALL in the head.
That being said, here is a short list of the NON HORMONE related reasons a woman's libido may not be matching yours:
1. Your expectations might be a bit much -- twice a day, every day, starts to be exhausting once the horny teens and 20s are in your rear view, especially when there are other things that consume physical and mental energy, like work, care for children, dealing with parents and in-laws, chores, and money issues, etc.
2. She's pissed at you or about something in the relationship and consciously or not this is how she's striking at you.
3. She's tired/Her job is wearing her out/The kids are giving her hell/The grass needs cutting/laundry needs washing/garbage needs to be taken out/dishes are piling up/the porch needs paint/the trees need trimming/the car's making a weird noise and any/all of that shit crowds out any thoughts of sex.
Now, assuming everything is totally, ecstatically hunky dory in your lives, and (THIS IS IMPORTANT, IF YOU IGNORE EVERYTHING ELSE, READ THIS) if she says SHE wishes her libido were higher and she's not happy, then she needs to find a doctor who specializes in hormone balance/HRT/antiaging. Doesn't have to be an endocrinologist, in fact, they (and gynos) are well, kind of stupid sometimes.
A physician who knows about women and hormone balance can look at her blood work, listen to her symptoms and work accordingly, safely.
Seriously, female hormone balance is NOT a do it yourself project. And just to clarify, ALL of the following hormones go into female libido (and there's more than these, but these are the big four): Progesterone, Estrogen, Testosterone, Thyroid. The slightest imbalance of the ratios of any of these hormones in relationship to each other, or just abnormal levels, low OR high, could impact libido.
You do NOT, I emphasize DO NOT EVER give a woman extra estrogen willy nilly. And estrogen is not female testosterone. Female testosterone is testosterone, just significantly less than the male body produces.
So the first step in figuring out how to increase your wife's libido is to sit down and talk to her about your sex life.