Can Pregnancy Happen Even After Taking Contraceptive Pill?

Doctor i had intercourse wid gf n i found d condom i used was torn. She had emergency contrceptive pill within 5-6hrs of intercourse.she had periods on 1st of december which was the normal cycle.aftr consuming the pill she again got periods on 15th of decmber.itz10th jan n shez nt yet got her periods.we had pregnancy test done and the result was negative. M worried if she gets pregnant. And whn wil she get her periods ?