Is it permissible for a fiancée to appoint one of her brothers or her maternal uncle to be responsible for her marriage contract, given that her father is mentally ill with schizophrenia and refuses her marriage, accusing her of zina (adultery/fornication)?

If the father is ill and has reached a state where he no longer comprehends, then his guardianship over his daughter is not valid, because sanity is a condition for a guardian. However, if he is of sound mind, his guardianship remains. But if he refuses to marry off his competent daughter, then he is considered to be hindering her marriage, and his guardianship falls away and transfers to the next guardian in line or to the ruler. It is advised to refer the matter to the Sharia (definition) court to examine the father's condition and to remove the harm from the girl by arranging her marriage. The maternal uncle cannot be a guardian.