What Causes Tiredness With Less Body Weight And Stress?

My sister is thirty-some years old. I'm a bit worried for her seeing how stressful her life is and how much she deals with on a daily basis.

For years, her health has been declining. She always feel worn out. She is very, very skinny. She weighs 95 lbs. and is 5" 3'. She eats a lot but as of late, she can no longer hold it down or forces herself to eat. She does eat healthily though. A few months back, she fainted in front of the house. ON a few nights, she can't sleep. I don't know what is going on and nor does she. But could there be some sort of rare genetic disorder or some other common disorder that we just happen to overlook.