I and my girlfriend had sex 3 days before her menstrual can she get pregnant?

Not very likely: The most fertile time for a woman is 14 days before the next period is due. Sperm can live inside a woman for up to 5 days. So 3 days before a woman's period is due is a time she is not very fertile and not very likely to get pregnant. That being said, unless you are trying to conceive it's best to use assume she is fertile and use some sort of birth control.