Thanks for your query.
Menstrual disturbances are known to occur with emergency pill.
Her symptom suggests she is having Dysmenorrhea.
Dysmenorrhea is the occurrence of painful cramps during menstruation
I suggest her to take any of the NSAID's for pain. If pain is severe then she has to consult a Gynecologist to rule out secondary causes of Dysmennorhea.
Dont worry. She is not pregnant.
Hope this helps.