Answer:
Years ago, there was a belief that a virgin would always bleed after her first intercourse, but modern science has shown that this is a myth. Many young women who are virgins do not bleed when they have intercourse, because there are several other ways for the hymen to break that do not involve sex. The best way to be sure about her virginity is to ask her: one would hope you are in a trusting relationship, and if so, she will be honest with you about it. If you cannot talk about such things with openness and compassion, your marriage may not work out.
But without being critical of you or seeming to question your priorities, there is something else to consider: the fact that a young woman may no longer be a virgin does not mean she is immoral or an evil person. Even the best people can make mistakes, and although their culture or religion says pre-marital sex is wrong, sometimes people fall in love and commit a sin. Ask yourself whether you truly love this woman, because if you do, you may want to forgive her if she made such a mistake. While virginity is very important in some cultures, it should not be the only qualification for choosing a wife.