Can a girl get pregnant 3 days after her period?

Yes: A woman can potentially get pregnant at any time during the menstrual cycle, even if her periods are irregular and unpredictable. 14 or so days after DAY 1 of your period is the most likely time for ovulation to occur and possibly the "best time" to try to get pregnant.

Yes: If you are having unprotected intercourse and ovulating you can get pregnant at any time. You can always ovulate early and sperm do hang around. Use protection unless you want to be a father.

Yes: A woman is typically infertile for 7 days after the start of her period. So if she is within this window, the chance of pregnancy is less likely ( but still possible)