We can’t tell you this, neither can you ever guess unless she tells you herself. Also the hymen can be torn or stretched in lots of ways even without having any kind of sex, in Sports like cycling horse riding, running to catch a bus. To Clear your doubts read more here: http://lovematters.in/hi/resource/faqs-hymen-and-virginity Are you saying that she can’t recall if she had sex or not? Is that the point? That is possible, no doubt yet there must be some signs of what went on the night past, no? What to do- I really cant say. Talk to her very openly and see what she says is return… On the basis of this, make your final decision, either you let it be- forget it ever happened– or then move on and find your sense of love and balance, elsewhere.