Hi Amita, Welcome to HealthcareMagic Forum.
It could happen if she is having progressive neck stiffness as result of spondylosis
or due to acquired torticollis
. She needs to take her medications regularly and go for regular follow up to her Orthopedist. If necessary Kindly get a repeat x ray neck or EMG done and get her examined to rule out if she has any neck muscle stiffness.
She needs Physiotherapy
It she does not respond to these measures, she may require surgery to relieve the pressure on the nerves or the spinal cord
I wish your Mother Good Health, Take Care.