Am I obligated to give a portion of my salary to my mother monthly, despite my need for the money and her desire to disown me if I don't, especially knowing that she is well-off, and would my refusal be considered a sin?

The maintenance of a poor mother is, by custom, obligatory upon her well-off children. However, if the mother is well-off and does not need maintenance, she is not entitled to anything from her daughter's money. Nevertheless, the daughter should be kind to her mother and give her from her wealth what does not harm her, due to the immense right of the mother and the virtue of honoring her.