What is the ruling of Islamic law concerning a daughter who stopped sending money to her mother after she used to do so regularly, claiming financial hardship despite not being married?

The maintenance of poor parents is obligatory by consensus. Therefore, the daughter and her sisters, whether married or unmarried, must provide for their poor mother. The share of each shall be according to her financial situation, as Allah Almighty says: "Let a man of wealth spend from his wealth, and he who has his provision restricted - let him spend from what Allah has given him." It is not permissible for any of them to withhold what is obligatory upon her of maintenance, if she is able. The sister who stopped her contribution is obligated to pay her share according to her circumstances. Furthermore, it is obligatory to treat the mother with kindness and maintain good relations with her, even if she is not poor, for her dutifulness necessitates Allah's pleasure.