It's bad enough the overthinking about ourselves but when it's our children, it's a whole different thing!
Being laid low with a head cold at this time of year is rubbish.
I'd start simple. Is she eating? Drinking? Has she had any kind of fresh air? Been in bed on her ‘phone, watching Netflix for a while week?
I have a nearly 18 year old daughter and when she's in too much she is grungy and groggy.
I would try and get her up, showered, downstairs, eating, doing anything other than screen watching got. Keep her dosed up on the paracetamol.
Hopefully she will start feeling better.
Incidentally, those screens play havoc with our eyes - does she wear glasses? Need an eye test?
Try not to panic. I know it's hard. Trust the GP and your own instincts which, as you say, are that it's not serious xxxc