Sister assuming legal guardianship of minor or retarded brother
28-2-2017 | IslamWeb
Question:
Assalaamu alaykum. I have one daughter and one son. My son is mentally retarted. My question is: can my daughter be the guardian of my son after my death, or should one of my brothers or nephews be his guardian?
Answer:
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no religious objection to appointing your daughter as the legal guardian of her brother. According to the agreement of scholars, it is valid to appoint a female legal guardian. The Kuwaiti Encyclopedia of Fiqh reads, "According to the agreement of the scholars, the legal guardianship of a person and property can be granted to a woman under the Sharia. It was narrated that ‘Umar 
appointed his daughter Hafsah as the executor of his will. Also, the woman's testimony is recognizable by the Sharia, just like the man's testimony; accordingly, women are competent for legal guardianship just like men."
If you do not appoint your daughter as the legal guardian over her brother, she shall not be granted the guardianship. The scholars underlined that the guardian over the minor and the insane person after the death of the father is the one whom the father appointed. If no guardian was appointed, then the Muslim ruler (or the one who acts in his stead, such as the judge) acts as his legal guardian. Some scholars, on the other hand, held that the guardianship is transferred to the closest relative if no guardian is appointed, and that the guardianship is not transferred to the ruler. This is the view which was declared to be preponderant by Shaykh Ibn ‘Uthaymeen 
. He said:
"The second view in this regard is that the guardianship is granted to the closest relative, even the mother if she is sane and legally responsible for her actions, because the purpose is to protect this child or insane or foolish person (Safeeh). If any of his relatives can shoulder this duty, then they are worthier of the guardianship. This is the correct view, Allah willing. Hence, the grandfather may be granted the guardianship over his grandchildren, the full-brother may be granted guardianship over his young brother, and the mother may be granted guardianship over her son in the absence of competent male relatives. Yes, if the relatives lack compassion, love, and kindness, it is then that we resort to the ruler to appoint an appropriate guardian."
Perhaps this is the optimal solution for Muslims living in non-Muslim countries, where there is no Muslim ruler to assume the guardianship over those minors.
Allah knows best.