What is the ruling on a husband officially authorizing his sister with a comprehensive power of attorney to dispose of his money, and does the wife have the right to request the annulment of this power of attorney due to the harm she incurs from it?

The agency is a permissible contract, and the husband may revoke it if he fears harm from the husband of the principal. It is permissible to inform him of this. As for the agent borrowing for himself from the agency's money, it is not permissible without specific permission from the principal. It is also not permissible for him to purchase for himself from his principal's money, according to the more preponderant opinion, due to the presence of suspicion. If the principal permits him, then it is permissible, otherwise not.