Is it permissible for a mother to curse her daughter, and what should the expatriate daughter do to help her elderly mother who wishes to return home to live with her other daughter who does not care for her?

Allah commanded obedience to parents and good treatment of them, and the mother's contentment specifically holds a higher status. If the mother is of sound mind and understands her actions, it is not permissible to refuse to fulfill what brings her contentment, such as allowing her to return to her country. As for the sister, she can be reminded to care for the mother, and one must be cautious of anything that displeases the mother.