Question 83: What is the ruling regarding a woman who fasts two days that she missed of Ramadaan without her husband’s permission i.e. without telling him. She felt shy to tell her husband. If it was not permissible for her to do this, should she expiate (offer Kaffaarah) for it?
Answer: A woman has to make up for the days that she did not fast in Ramadaan even if it is without her husband’s knowledge… read more here.