That's a pretty unlikely pregnancy scenario. You need a good application of semen to her vagina before starting to worry. She is not telling of any other early pregnancy signs. Maybe she is late because her hormones got upset by the sexual excitement. Now that her period is late a home pregnancy test would quickly set your fears to rest.
Please get your hands on some condoms to reduce future risk, and have her download a period tracking app so she can get a feel for her most fertile days. Sex in the week or ten days before her period is due is the safest.