In my opinion itching is not due the medication. As your mother is a diabetic patient and is known as a Silent killer. It has effect on Kidney
. You must do her Renal function test and if B. urea is raised than itching is due to that and you need to treat that. Consult you nephrologist
Otherwise you can try calamine
lotion or aleovera for local application. Make a list of food or substance which cause or increases your itching and keep yourself away for that.
specialist opinion can be taken if this is due to roughness of skin.