Is it that your daughter doesn't recognize their faces ( Prosopagnosia) or is it that she doesn't remember any of the people or anything about them any more? I think facial agnosia can happen after TBI too but from your first post it sounds as if it's more than that.

I would echo the suggestion regarding a Neuropsychologist.

edited to add: personally, if it was my 10 year old daughter and she had memory loss as bad as you describe and she was only 4 or 5 days post concussion I wouldn't have her going to school. I'm wondering why her doctor would suggest such a thing.

btw there is a lot of info regarding amnesia following head injury online.