If she’s had full bloods that were normal, it rules out most serious causes (like inflammatory disorders, cancer, diabetes, thyroid problems, infections, anaemia, autoimmune conditions).
Sounds like she’s not eating well. Why does she always skip breakfast? Is she underweight, overweight? Does she eat a nutritious diet, exercise regularly, take vitamin supplements?
After 6 months and with no clear symptoms, it would be U and a waste of time to go to A&E with a list of vague chronic symptoms, when she’s had full bloods, is awaiting a glandular fever test and has been seen by medical professional recently.
Glandular fever is horrible and if that’s positive it will give an explanation… but there’s no cure, she just needs time to recover and rest. The nurse who felt her tummy was probably checking for signs of an enlarged spleen (can be a sign of glandular fever).
It doesn’t sound like an emergency so taking up the time of emergency services seems wrong. In A&E what do you think they’d do, other than refer her back to her GP?
Lots of teenagers suffer from anxiety/depression/stress which can cause loss of appetite, pallor, lots of hazy physical symptoms that don’t add up. If you can I’d get her seen by a private psychologist. There may be an underlying MH cause.
Considering all NHS services are so understaffed and underfunded at present, and about to get worse with winter pressures and Covid still hanging about, I think you need to be more patient. Diagnosis and treatment are delayed for most people, unless doctors think the underlying cause is serious.