Does it really matter that much to you that she is a virgin? If so why?
Have you considered that you may have projected YOUR need for her to be a virgin and she doesn't want to be rejected by you?
If you want this to be long lasting the worst thing you can do is allow your standards and expectations to cause her to need to be less than truthful to you.
Society has screwed sex up completely so please don't let those standards destroy something that could be great regardless of her virginity.
Can you accept her the way she really is? Even if that means she has been with one or a dozen other men? Or would her lack of virginity be a deal breaker for you?