Poor child I expect she feels so bad, I see they are doing tests so hopefully they will figure why she is so sick, meantime I suggest some pureed fruits, she may have a sore throat so anything soft would be good, lots of liquids, scrambled egg , if she is up to it let her feed herself as
children like that ,
for weight get her on a high fat diet, whole milk ,whole milk cheese, smoothies are good puree any fruits and add crushed ice and whole milk , cereals soaked in milk so they are soft.