Is it permissible for me to make up my mother's fasting days on her behalf, knowing that she owes sixty days of fasting and postpones making them up year after year?

It is not permissible to fast on behalf of a living mother or any other living person. If someone fasts on her behalf during her lifetime, it will not suffice her, nor will it relieve her of the obligation. If the mother is able to make up the fasts but is too preoccupied, she must be advised to start making them up immediately. She is also liable for an expiation for delaying the making up of the fasts for each day if the delay was without a valid excuse.