Question

she eats very little; nevertheless, she does not lose weight

Answer 1

just because she eats a little bit of food means shell lose weight , when she stops eating she's not getting the proper vitamins so her body goes into this kind or shock and starts storing all the food which eventally turns into fat

Answer 2

if she stats eating a little bit more her body might stop storing the food. after that she needs to go onto a steady diet and exercise.