As above, I don't think supplements are the answer.
Rigid control of BG levels is the best way to reduce or avoid complications.
You don't say how old your mother is, or if she is living independently or being cared for.
Above a certain age the BG targets for T2 diabetics are relaxed a great deal because of the difficulty in maintaining a strict regime; all sorts of issues including other complications of old age which may impact on the maintenance of diet, exercise, and carefully controlled medication.
Cynically (moi?), this may include the background thought "At that age you haven't got much to look forward to. Just enjoy yourself in your little remaining time".