This sounds so much like what my 26yr old son has just been through!
He started with feeling yucky, and then very high fevers, we took him to the ER on the Sunday, they said very bad tonsillitis, gave him meds and sent him home, but the Tuesday he was worse, took him to our doctor, said very bad tonsillitis, gave him more meds and sent him home
By the Thursday morning, I started to panic as he was even worse, we couldn't get his temps down and he hadn't eaten for over a week, and now couldn't drink either, called the doctor who sent him to an ENT... ENT admitted him to hospital immediately.. he was very, very ill!
He was put on steroids, and antibiotics via a drip, given pethidine in his drip and oral pain killers that are so strong they give them to cancer patients!
He stayed in hospital for about a week.. can you believe?
They also said there was an underlying virus, did numerous tests, but couldn't find out what it was.
He has been home how since the 16th December, still didn't eat for days, and was very, very weak. He is improving now, at last.. is eating fairly well and slowly getting his strength back.
He goes in to have his tonsils removed on Thursday the 10th
Perhaps your daughter does need to be hospitalised... I hope she improves soon, I know what she and you are going through.
Hugs and best wishes.