As she is having these irregular periods
of late, she should be investigated and examined properly. The cause should be identified. You should get her blood tested for serum beta-hCG levels and also get a trans-vaginal sonogram and consult a gynecologist. Sudden weight disturbances, stress, infections, certain medications, polycystic ovaries
etc. are some of the reasons for abnormal periods. Please use contraception
to avoid any unwanted pregnancies. Hope your query is answered. Take care.