How does a woman appoint her brother as her agent in a marriage contract, and what is the legal wording for this agency? Does it require witnesses? Is it a condition for the imam of the mosque to hear the woman's wording of appointing her brother as her agent?

The brother is entitled to the guardianship of his sister's marriage if there is no guardian more deserving than him. Her consent to the marriage is sufficient without needing a proxy or witnesses, provided he is the most deserving guardian. If there is no guardian or legitimate judge, then the woman may appoint a righteous Muslim man to marry her off. This appointment is confirmed by the testimony of two righteous witnesses, and the proxy is valid with any expression that indicates it.