Hi there...I can understand your concern. From your description it looks like your mother is having gangrenous changes in the left index finger. Gangrene occurs due to necrosis of the cells, that is, the cells are dead. There is no way to revive the cells/tissue once they are dead. She will need removal of the gangrenous tissue as soon as possible becaude it can spread depending on the etiology for gangrene. So kindly consult a good general surgeon or vascular surgeon or plastic surgeon for further evaluation.