she did not get her period as well as withdrawal bleeding

had unprotected sex with my gf on 14 Mar, She had an unwanted 72 within 50 to 55 hours after intercourse. her regular periods date is on 28th Mar. its 31 Mar but she still did not get her period as well as withdrawal bleeding.. is it okay? does she need to do a pregnancy test? if yes within how many days? within how many days after having unwanted 72 do girls get their withdrawal bleeding? please please help! m tensed..