Is my mother's Hajj valid, given that she combined the Ifadah and Farewell circumambulations (tawaf), stayed for two days in Mecca, then departed after assigning someone to purchase some necessities? And is there any expiation (kaffarah) due upon her, and what kind is it?

The majority of scholars view the Farewell Circumambulation (Tawaf al-Wada') as obligatory for those who are not menstruating, and their evidence is the hadith of Ibn Abbas (may Allah be pleased with them both): "The people were commanded that their last act should be with the House (Kaaba)." They differed on whether the circumambulation must be the very last act before immediate departure or if it is permissible to stay for a few days afterward. The Shafi'is and Hanbalis held that it is not permissible to stay except for the purpose of fulfilling a need or purchasing provisions. Accordingly, if a woman misses the Farewell Circumambulation, she is required to slaughter a sheep to be distributed among the poor of the Haram, because she neglected this obligation. As for the Circumambulation of Ifadah (Tawaf al-Ifadah), it has already been performed.