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Emergency contraceptives can be taken within 72 hours of unprotected intercourse. Consider getting her evaluated by a gynecologist to make sure that she has no underlying health issues that can be made worse by taking emergency contraceptives (as they contain high doses of hormones). It will also help to decide which one is best suited for her.
If you intend to be sexually active, she should consider getting started on regular birth control to avoid unwanted complications from repeated high doses of hormones from emergency contraceptive use.
Take care.