Well my daughter is 10.
And whenever her neck hurts... it generally means that she is getting sick.
It could be a cold or any kind of bug.
But whenever she is sick, or getting sick, her neck (the back of her neck) starts to hurt.
Maybe one time, it was a stiff neck from sleeping.
Take your little one to the Doctor.
A sore neck, can also be Meningitis. For example.
Don't take her to a Chiropractor yet.
Take her to the Pediatrician, first.
Advil for kids, and an icepack on her neck, for now.
But take her to the Doctor.
Her neck pain is probably, the muscles.
Not the spinal bones.
Or it could be a simple kink in her neck/muscles.
Who knows.
Don't manipulate her neck. Because it can make it worse.