Is it permissible for a Muslim woman to dispose of money given to her by a Christian woman for feeding cats, and instead spend it on the poor and needy, without the Christian woman's consent?

It is not permissible for a Muslim woman entrusted by a Christian woman to manage her wealth to violate the terms of the agency, even if her action would be more beneficial. If she violates them, she guarantees the wealth, because an agent's action that contravenes the principal's instructions is considered an unauthorized act. If it results in harm, she guarantees it, and her action is not effective. If the wealth is lost, she guarantees it.