Hello,
Protected sex prior to period is very much safe and literally there is no chance of
pregnancy. Though, she needs to confirm it with one home pregnancy test with urine.
Other reasons for delayed period are
hormonal imbalance, stress/ anxiety,
thyroid problem,
ovarian cyst, wt gain/extreme loss, irregular eating habits, psychological factor etc.
Here, she may require some investigations to rule out underlying pathology through USG pelvis scan, thyroid profile & other hormone assay etc. Consult with your gynecologist and take suggestive measures.
Avoid stress / anxiety, take healthy diet with vitamin &
iron supplements, eat more fruits & vegetables , drink plenty water or juice and maintain genital hygiene properly.
If you need further consultation with me, then you can visit http://www.healthcaremagic.com/doctors/dr-soumen-patra/63326.
Take care yourself.