... well, after all she was a virgin when you got married. So, maybe when it comes to sex, she's shy and/or doesn't know what to do. And, then there are those who for whatever reason, just aren't into sex. Have you considered marriage counseling to sort any possible underlying issues?
You have mentioned that she wanted to remain a virgin until marriage. Maybe it can reveal something about her attitude to sex in general, maybe her wish was caused by something which has also other impacts on her attitude to sex in general and on her sexual behaviour or inhibitions. For example, if it was caused by some religious system, this religious system could have had some significant impact also on her inhibitions in sexual behaviour in general, also in marriage.
It´s just one possibility, maybe not the real cause in her case. There are countless other possible causes - e.g. hormones, low sex drive, side effects of contraceptive pills etc as mentioned in the previous post.
First and foremost, I would say to try to get rid of the pressure and stress of sex. Just the fact that you are worried about it can make it worse for her. And I know that is MUCH easier said than done as I'm the one in your shoes currently. I will be 30 this year and my husband is 31, and I want sex all the time, and he is definitely not as interested as I am. Talk about frustrating! But from all that I have read, it's worse when we stress it (almost like performance pressure).
When I was younger though, I had the very same thing happen. I went to the dr. because I thought there was something wrong with me. And it was after I had been in a relationship for a few years myself. They told me that there is nothing at all wrong with me, and this happens sometimes and is completely normal. There can be so many things that cause this. Definitely hormones could have a lot to do with it. Is your wife on birth control of any sort? Sometimes (oftentimes), the hormones in birth control can totally wash away a woman's sex drive. Also, many other medications can do it (namely, depression/anxiety meds). If she has a lot of stress in any other area of her life, that will ABSOLUTELY cause a decrease in sex drive. In my case, that was the issue. I was stressing about the house not being clean enough, work and money and blah, blah, blah. It affected me.
Try to help your wife relax as best you can. Help her clean the house, cook her a dinner. Maybe get a warm bath running for her with some candles. Give her a massage. Try to just take her away from the real world for a bit. That may help. If it really seems bad, or if she can't deal with it anymore, have her go to the dr. They can check her hormones. If they are way out of whack, they can help her. Also, if she is having a hard time "getting ready," there are many products that you can use that can help that too.
Just be patient with her. It will eventually get better.