Suggest Ways Of Avoiding Pregnancy

Hi on 07th march 2014(11.00 pm), I had a unprotected sex with my girl friend,she took I pill within 2 hr of sex,On 8th march(yesterday night 11.00 pm),we again had unprotected sex,Please guide is it safe to if my girl friend take as another i pill within next 24 hr,to avoid pregnancy or taking I pill once will do ???, also usually she has periods between the date 10-15 of every month .please guide to avoid pregnancy ??? is there any chance to become pregnant under given circumstances