What Causes Delayed Periods After Taking Idoz 72?

Hello, me and my girlfriend had sex on 17th Feb and c had idoz72 within 48 hours. C had her menstruation on 27th Feb which i think was a normal when comparing and calculating to the last month period. It is already 30th March and c has had no any period. Is this happening because of the emergency contraceptive idoz72?? Is it fine to take pregnancy test now since this is the time of menstruation of her?? Will it give the right result?