Is it permissible for a woman whose husband has passed away to complete her 'iddah (waiting period) in her father's house instead of her husband's house? And what are the necessities that permit a woman to leave her house during the 'iddah?

A woman observing her 'iddah (waiting period) is not permitted to leave her marital home before the 'iddah expires. This period is four months and ten days if she is not pregnant, and until she delivers her child if she is pregnant. However, she is allowed to leave for necessity, such as fear for her safety, or if the place is uninhabitable, or for her essential needs for which she cannot find anyone to fulfill, such as earning a livelihood or seeking medical treatment.