Thank you for your query.
I can understand your dilemma. Without seeing the type of movement being described by you it is difficult to tell the reason for it. As it started around 6 months of age and has recurred now I suggest you consult a neurologist
and, if possible, a pediatric neurologist to rule out the possibility of some form of minor convulsive disorder
. The neurlogist may even order a MRI
to know the condition of the bones in the neck.
I hope I have answered your query to your satisfaction.
Wishing your daughter all the best.