Hello there. The normal menstrual cycle can be of a range from 14 days to 40 days so a little delay is normally also seen so you don't need to worry as such. Other causes could be hormonal imbalances like thyroid issue, poly cystic ovarian syndrome, stress etc. Kindly get a few tests like thyroid profile, ultrasound of abdomen and pelvis done. Revert with reports or consult a gynaecologist in person with reports so that she can do the needful further. Once a cause is established, treatment can be started. Don't delay any further. BEST regards. Dr. Anil Kumar Jain