[Concerning the Waiting Period]

Answer—and Allah grants success: What appears to me—Allah knows best—is that it is a right of Allah Most High and of the husband. It is a right of Allah in that He—Exalted is He—commanded it and made it obligatory upon women; for this reason the scholars said that intention is required in the waiting period and that it begins from the time of knowledge. Thus, if a husband dies and his wife does not learn of his death until a year later, it is obligatory upon her to begin the waiting period for widowhood from the time she learned of his death, and she does not count the year that has passed.
And it is a right of the husband because of the husband’s right over his wife in safeguarding his lineage (his “water”), and because of what is legislated within the waiting period of ihdād (mourning), which means manifesting grief at the husband’s separation.
The waiting period is the abstention and waiting of three qurūʾ, or three months, or until she delivers (if pregnant), or four months and ten [days].
Remaining in a particular place is not part of the meaning of the waiting period; rather, it is something else that attaches to the waiting period, and likewise ihdād is among the concomitants of the waiting period.
A woman divorced with a revocable divorce—Allah Most High has granted her the right to observe her waiting period in her husband’s house. As for a woman divorced with an irrevocable divorce, she has no right to observe her waiting period in the husband’s house.
A woman whose husband has died may observe the waiting period wherever she wishes—in her own home or in her husband’s home; and it is said: she must observe it only in her husband’s home.
What appears to me is that the woman in waiting observes it in her home, and she may go out for a valid excuse.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1