Constant head movement

My daughter is 28 years old and was born with spina bifida, myelomeningocele, hydrocephalus. She as always had some type of constant and unconrollable head movement whether it be up and down or as now a rhythmic left to right swing of the head. The urge to move her head wakes her up at night and she has to sit up and move it. Sometimes it is a slow rhythmic movement at other times it is so fast that we gently tease her to slow down lest her head roll off. There are times she can slow the progress of it or hold it still if she is intense on concentrating on something. She also had a vp shunt and a few years ago when the shunt malfunctioned and the pressure built up in her head she did not shake it---however once the new shunt was installed and the pressure began to return to normal the head shaking resumed. We would appreciate any information anyone may have on this subject as we have yet to see it in anyone else. Thank-you,
Theresa