What Causes Delayed Periods After Taking I Pill?

me n my girl friend had oral sex on 31st July, 2011 , but i touched her vagina with my penis for once or twice. Am not sure if my precum entered to vagina. But within 72 hours i gave her unwanted 72 . The problem is she is having periods on 4-5 of every month. As its, 8th of august , but she didn't get down. She was also suffering from hormonal disorder few years back. Suggest me what can we do no ???