question from my friend

Okay so here are some questions, After you stop taking bc will your period be late the first time without taking it? & she witnessed some bleeding and thought it was her period, she stopped taking bc like 3 weeks ago & she woke up this morning and it wasnt. Could this be from rough sex or implamation bleeding? She said it was a lot of blood that looked like her period. Is it very possible she is pregnant because he nutted in her on her most fertile day ?