When Can I Expect Periods After Completing Femilon Course?

Hi! My wife was prescribed Femilon contarceptive tablet 21 day course. However, we had unprotected sex during the same period quite a few number of times. Now since the course dosage is over & she is going through a withdrawal period, I would like to know is there any chance of getting pregnant during the period? Also when can she expect the periods to start since she has stopped the pills couple of days back after completing the full course?