Hello, I have gone through your query and understood the concern. I would like to inform firstly that any intercourse that takes place during the safe period of a menstrual cycle carries very little risk of conception. If she was in her safe period during the period of intercourse, she is naturally protected. Let me inform you that emergency contraception taken within the stipulated time interval offers very good protection. Repeated intake, especially within the same menstrual cycle creates hormonal disturbances. this is the cause for the absence of the bleeding. Please get further help if she becomes overdue by ten days for her next period. The pill use should be restricted to once or twice in a year. Hope this helps.