Greetings, I Will Be Having Sex With My Girlfriend This

Greetings, I will be having sex with my girlfriend this weekend. She is saying that she had never had sex before. But somehow I have some doubts about that. She has been shy since the very beginning about the sexual part of our relationship (such as being shy when I touch her breasts, butt etc.) and told me that it felt weird when she first touched my penis. I want to believe in her but I still have some doubts. How can I tell if she is a virgin? Thanks.