I am utterly disgusted that there is clearly something not right with your daughter, but these so called medical professionals keep shrugging it off as 'viral'!
Obviously I'm no expert, but I agree with you that it could be anaemia. All it would take is a simple blood test to confirm and then she could be treated. I don't understand why they won't do one? And heaven forbid if it turned out to be anything worse, and they're just ignoring your concerns. Do you have an out of ours service where you are? I'd be ringing them on a weekend and trying to get an appointment, see if they handle things differently to your GP. On top of that, I'd be looking in to changing practices as I'd completely have lost faith in them by now.
I'm going through a slightly similar situation, in that my son has had a medical issue for a year now that has still not been resolved. We took him to the GP in February 16 after we noticed lumps in his neck (one quite large) which weren't just flared up because he was ill, and don't go down. He has seen a consultant twice, had an ultrasound, been to the ENT clinic and was supposed to be having a fine needle biopsy. This was never done and he was last seen at the hospital in August! We've just now got a consultant appointment through for 1st Feb, so I'm hoping we may get some answers soon, and nothing sinister has been going on and not been dealt with.
I hope you get some answers soon and you can get your daughter back up to full health. It must be so awful for you seeing her like this and nothing you can do xx