Is it permissible for a mother to reject a suitor for her daughter due to lineage, preferring it over his religious commitment and character, and what should the daughter, who is attached to the young man, do in this situation?

The mother's objection to her daughter marrying a man of good character and religious commitment, her cursing his family, and her preference for lineage over religion, is impermissible. She must repent. The daughter must ask her guardian - be it her father, brother, or another - to marry her to this man. If he agrees, then she should marry him, and this will not be considered disobedience to her mother. If the guardian refuses to marry her, there is a method to address such an obstruction (عضل) mentioned in Fatwa no. 93368.