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If the date of her period was 19/03/2011 then the next date should have been around19/04/2011 if the periods were regular.Since due to sex she took I-pill which is a hormonal
pill used for emergency contraception
she got bleeding on 02/04/2011 which was a breakthrough bleeding
due to I-pill.So if the periods are not disturbed due to I-pill then hopefully she should get periods around 02/05/2011 with a acceptable delay of 4-5 days.If she does not get her periods by then please consult a Gynaecologist for opinion and treatment.