The causes for this kind of a problem are many. A few of them are as follows:
1. Cervical spondylosis
2. A high blood pressure
causing a TIA
or a stroke
compression due to local causes or due to Diabetes
4. Ankylosing Spondylitis
All these need to be ruled out in her before starting the right treatment.
I would suggest you to get your mother examined by a Neurologist
and get investigated for these problems and treated accordingly.
I hope this gives you an insight into your mother's problem.
I wish her quick recovery.