My girl friend’s periods normally having on 9th of every

Patient: My girl friend’s periods normally having on 9th of every month. I had sex with her on 7th (before 2 days). But she didn’t get her periods yet. It’s already 3 days late. We are afraid of getting any pregnancy. Please let me know is she can get pregnant? If there any way to get avoid from it. ? Why is she getting late for her periods .. ?

Doctor: