Hi, Welcome to Health care magic forum.
Your 14 year skinny girl want to become fatty, immediately.
As you describe, she must be having
anemia, worms in the intestine, or some chronic disease.
I advise you to consult a physician for diagnosis, and treatment accordingly.
I usually prescribe to my patient with such symptoms injection of anabolic
steroids, periodically,
protein supplements,multivitamins, and hematinics.
Give her more of green leafy vegetables, pulses, sprouts, and protein rich foods, to have a early recovery, and to have good resistance.
Wishing for a quick and complete recovery. Thank you.