possible pregnancy the next day she felt sick

It is for all practical reasons impossible for her to get pregnant from that.

Most women is infertile while on their periods, semen does not travel well through panties and boxers, and she must have had a pad or tampon that further stopped your semen.

She likely felt sick the next day because of her period. Women have all sorts of bad feelings before and during our periods. Pain, cramps, headaches, nausea, back pain, tired, lack of sleep, weight gain, emotional, angry, sore breasts, oily hair, achne, hungry, no appetite and all sorts of other aches and pains. As her how she feels when her period is there so that you can know to treat her very special on those days.

Take care!
Please be careful though!