Hello Good Evening,
Your friend has missed period, which is due to some common reason like:
-Stress and anxiety
-Excessive weight loss
, or weight gain
Any of them can be a cause for your missing period, so please go through proper evaluation to get the causes like hypothyroidism or PCOS.
Another rare possibility is premature menopause:
In rare cases, a woman's ovaries stop working at a very early age, ranging anywhere from the age of puberty to age 40, and this is known as premature ovarian failure
(POF). Spontaneous premature ovarian failure affects 1% of women by age 40, and 0.1% of women by age 30.
So go for a USG, TSH and other investigation to find out the cause of amenorrhoea.
Her symptoms like extremely exhausted, poor appetite
are interrelated to the etiology, and might be hypothyroidism, so please get her evaluated.
Dr. Naresh Jain.