and infections result in disturbance in control of blood sugar level,but in your mother's case,it looks to be due to secondary beta cell
failure of pancreas
In long standing diabetes
,the mass of functionally active beta cells in pancreas gets reduced gradually and a stage comes when no insulin
is made and released by pancreas even after giving higher doses of oral anti diabetic drugs.Your mother seems to have reached that stage.
She is a type 2 diabetic but insulin dependent.She won't be called as type 1 diabetic patient.
Most likely,She would have to take injection insulin for rest of her life.
There is nothing wrong or bad in this.Rather blood sugar levels would be controlled much better with injection insulin.