In this case, chance of pregnancy
is almost nil. You did unprotected sex on safe period (around period due date) if her previous cycle was regular. An other thing, she took i-pill additionally for extra protection. It is effective more than 58% after 48 hrs.
Period is delayed due to effect of the pill. She will get a withdrawal bleeding within 7-10 days. If she does not get it, she should undergo one home pregnancy test or blood test
to exclude pregnancy.
Consult with your gynecologist following test report. Practice safe sex