Praise be to Allah.
It is permissible for the woman who is observing ‘iddah following the death of her husband or following an irrevocable divorce to go out during the day to visit her sick mother, on condition that she goes back home at night and spends the night in her own house.
The basic principle regarding that is that it is permissible for her to go out during the day, if there is a need to do so.
Visiting her sick mother is a need that is recognised according to Islamic teachings, because of what it involves of comforting and honouring her mother.
Please see the answer to question no. 152188 .
The scholars of the Permanent Committee for Ifta’ were asked:
My mother is currently observing the mourning period after the death of my father – may Allah have mercy on him. During this period, my mother wants to go to see her elderly mother, to visit her in her house, because she is not able to go out due to her advanced age. Please note that the house of my grandmother, my mother’s mother, is not far away; it is in the same residential neighbourhood.
My question is: is it permissible for my mother to go out of the house to visit her mother? Please note that my mother has previously gone to visit her mother several times during the mourning period. Has she sinned by doing that?
Answer: There is no reason why the woman in mourning should not go out of her house to meet her needs by day, not by night. Visiting her mother who needs her visit is one of the greatest of needs, if that does not require travel, because it was narrated from the Prophet (blessings and peace of Allah be upon him) that he granted a concession to women in mourning allowing them to gather during the day to find comfort in one another, and to go back to their houses at night. It was narrated that Mujahid said: Some men were martyred on the day of Uhud, and their wives came to the Messenger of Allah (blessings and peace of Allah be upon him) and said: O Messenger of Allah, we feel lonely at night; can we spend the night at the house of one of us, and then in the morning go back to our own houses? The Messenger of Allah (blessings and peace of Allah be upon him) said: “Meet and chat in the house of one of you, then when you want to sleep, let each one go back to her own house.” Narrated by ‘Abd ar-Razzaq and al-Bahuti in as-Sunan al-Kubra. And Allah is the source of strength. May Allah send blessings and peace upon our Prophet Muhammad and his family and companions.
Standing Committee for Academic Research and Ifta’. Shaykh ‘Abd al-‘Aziz ibn ‘Abdillah ibn Baz, Shaykh ‘Abd al-‘Aziz Al ash-Shaykh, Shaykh ‘Abdullah ibn Ghadyan, Shaykh Salih al-Fawzan, Shaykh Bakr Abu Zayd."(Fatawa al-Lajnah ad-Da’imah 20/476).
But if the woman has received a revocable divorce, then her going out depends on the permission of her husband, because the woman who is revocably divorced is still a wife, with the same rights and duties as any other wife.
It was narrated from Ibn ‘Umar that he used to say: If a man has divorced his wife once or twice, she should not go out of her house except with his permission. Narrated by Ibn Abi Shaybah in his Musannaf (4/142).
And Allah knows best.