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Your M.I.L. may be suffering from Alzheimer Disease or as you put it she may have had a mental break down.
Please try to prevent alcohol reaching her and be especially careful to keep all medications out of her reach. She should be given medication under supervision of a medical expert
and by a responsible person in the household and do not permit her to take medicines on her own. Incidences are known when they take too many pills not remembering that they have already taken the pill, leading to very serious conditions.
She needs constant monitoring and do consult a Doctor for her ailments.