welcome to healtcare magic forum,
according to your description your sister seems to be suffering from urticarial rashes,in diabetes
its an common symptom .but need to confirm.
will suggest you to consult a homoeopath who will take care of diabetes as well this condition , homoeopathic medicines are very safe , effective and natural and will take care of all problems .
or for more info you can write down to ( firstname.lastname@example.org).
take care.wish you good health always .