What Causes Delayed Periods After Taking Birth Control?

My girl friend had her periods on Feb 18th and I had unprotected sex with her on March 1st. Though I did not cum inside her, for protection sake, she took an I pill within 7 hours. She had bleeding 5 days later and had that for a week till around march 13th. Now it is already March 24th and she has no early signs of periods.
Please advice. Should she get a pregnancy test done ?