Me and my girlfriend had sex but I didn't ejaculate inside of her, but my sperm was on her vagina(during her period). Later that night, she wiped to check if sperm was on her vagina, and she realized that when wiping in an upward motion, she wiped the sperm all on her vagina. Is there any chance of her getting pregnant? If so, then how do I prevent fertilization? It's only been two days since the incidence.