No, it's not a safe method of contraception. The pill works by following the menstrual cycle, and it takes some time to settle into the system and commence working efficiently. Even missing one day can affect the accurate function of the contraception, so this hit and miss method is virtually useless as a contraceptive. If your friend has not conceived, it is not because of her pill, and she is playing with dangerous odds. Tell her to contact her GP or FPC to discuss alternative methods of contraception.