It seems that she might be having osteo-artheritis in her cervical vertebrae
giving rise to irritation and pressure on nerves giving rise to this problem.
Go for x-ray cervical region.
Consult orthopedic surgeon and get examined.
If cervical spondilitis is found then she should go for,Physiotherapy
Short way diathermy,
Cervical traction, as advised by surgeon.
Avoid keeping pillow under neck while sleeping.
Ok and take care.