Should the grandmother eat from the halal meat brought to her by her grandson, and should she atone for her oath in which she swore not to eat meat, knowing that she is over ninety years old and her children provide for her?

If the grandmother swore not to eat meat, thinking it was donkey meat, and then it became clear that it was permissible meat, she does not break her oath and there is no expiation upon her. This is because the reason that led her to swear (the assumption of unlawfulness) has ceased to exist. This is known among the Malikis as "bisat al-yameen" (the basis of the oath) and among the Hanbalis as "al-muhayyij li'l-yameen" (the stimulant for the oath). The "bisat" is the underlying reason for taking the oath, and when it is removed, there is no breach of the oath. Intention affects the oath by specifying or generalizing it, and the reason takes the place of intention when the latter is absent.