Two years ago my father became the guardian (Wali) of a Muslim American lady. She talks a lot with him by phone and does not always stick to necessary questions, and does not speak with a firm voice, but as if she is speaking with a girl. This situation causes my mother a lot of problems. I want to know the nature of the relation between the Wali and the woman who is under his guardianship.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. If the guardianship of your father over this woman is limited to helping her in her business and protecting her from any harm that could affect her life, so he will be rewarded for that. As the Prophet Muhammad (Blessings and peace of Allah be upon him) said: "Muslim is the brother of another Muslim, he should not oppress nor should be hand him over to evil. Whoever fulfills his Muslim brother's needs, Allah will fulfill his needs. Whoever removes the trouble of his brother, Allah will remove one of his troubles on the Day of Resurrection and whoever covers up the fault of a Muslim, Allah will cover up his fault on the Day of Resurrection." [al-Bukhari and Muslim]. If this guardianship is limited to becoming her guardian during marriage, this is lawful since her parents and agnatic relatives next-of kin are not Muslims. But in both cases this man is alien to her, so he should limit his relation to her to the minimum necessary and avoid long talks with her as the Prophet Muhammad (Blessings and peace of Allah be upon him) said: " the Satan floats inside the body of a man along with the circulation of blood." [Narrated by al-Bukhari & Muslim ]. This woman should learn the Islamic morals and decencies as concerned talking to alien men. She should not soften her voice too much. We would like to advise you father to be ware of the Satan as the latter might sometimes influence the person through obedience to righteous deeds by pushing him to commit a greater sin. So, your father should avoid everything that could lead to such a tumult. Allah Says (Interpretation of meaning): (O you who believe! Follow not the footsteps of Satan and whosover follows the footsteps of Satan then verily he (Satan) commands indecency and wicked deeds). [24:21]. Allah knows best.