Hi & Welcome. I can understand your concern. In this scenario pregnancy is unlikely. Nothing to worry about it. There is absolutely no chance of pregnancy as her period was just ONE day after having unprotected sex and that too with pull out method . Physical intimacy during the later part of the menstrual cycle is not the fertile period to get pregnant, if her cycles are regular. Delayed period could be due stress, emotional disturbances, hormonal imbalance or some underlying medical illness. So you need not to worry. Adopt here afterwards safer sex like using condom to not only prevent unwanted pregnancy but also to protect yourself from sexually transmitted diseases. Take care.