What Causes Delayed Periods Post Intake Of Unwanted 72?

Hi I had sex with my gf on 19th dec, but her period date is 11 dec . On 19th we had sex At noon 1pm and she took unwanted 72 on tat day evening. And she gets period on 26th DEC tat too only one day little bleeding. Her age is 21.. But her regular period has to get on Jan 12 but still she dint.. Wat about pregnancy? And her periods delayed? Wen will be next period??