Thank you for your query.
After tubal ligation
, chances of pregnancy are very remote.
What is worrisome is that if she gets pregnant, chances of an ectopic pregnancy ( outside the uterus ) are very high.
So please get a pregnancy test at the earliest.
If negative, then the reason for such irregular cycles could be her age, as she is approaching peri menopause
Other causes are stress, anxiety, weight gain or weight loss
, thyroid imbalance, diabetes, polycystic ovaries
and endometrial lesions or hormonal medications.
in any case, its best to consult a gynecologist.