The problem your mother is facing is not too uncommon in diabetic patients. The commonest reason being the medications she is taking. I presume she must be on Insulin- there are certain types of insulins which are more probe to cause hypoglycaemia than others. If its the case, the insulin dose either be reduced or changed promptly. In addition to the insulin, there is another group of medications which can can cause low
sugar - she must on it then . Sometimes low sugars could be due to mismatch between the diet , medications and the exercise.
The success of the diabetic treatment depends not only on reducing high sugar levels but also preventing hypoglycaemia. This does not seems to be happening in your mothers case , hence there is a need to change the treatment your mother is on at the moment.