My sister is suffering from extreme cold intolerance, she feels extremely chilly even though the weather is very hot outside (peak temperature 42 c or 108 f today). she won't come out of her blanket and constantly has the heater on in her room?

Wonder about hypothyroidism, or even a congenital dysautonomia. Some medications could cause this, and indeed, could consider an emotional disorder. Have your sister see her doctor, get blood testing, and referrals if appropriate. This needs to be managed ASAP.

Cold intolerance can be a sign of severe thyroid insufficiency, or even severe infection or lymphoma. She needs to be seen by a doctor and have some bloodwork done.