From your description- it looks like the lymph
glands in the neck are swollen.
Usual cause of such swelling of the lymph gland is infection in the scalp/ ear lobe/ facial skin.
It can happen in infestations of the scalp- lice and also in dandruff
due to repeated scratching and secondary infection.
Since you say she is unable to move her neck, I would suggest that you see your Pediatrician
and get her examined. Your Doctor will examine her throat, ear, scalp, skin on face etc and if any infective focus is seen, he will advise treatment accordingly.
These lymph glands can be swollen in some viral infections and some other conditions too.
So please visit your pediatrician`s office and get her treated.
Till then you may give her pain killers like Acetaminophen
according to her weight.
Hope my answer helps you.
Wish your daughter a speedy recovery.