What is the ruling on disposing of the salary of a grandmother who has lost her mind, and is it permissible to use it to meet the family's financial needs or for marriage, knowing the difficulty of repaying what has been spent from it previously?

If the grandmother is of unsound mind, her property is interdicted, and it is not permissible to dispose of it by dividing it among the heirs as long as she is alive. The property is held until she recovers or passes away, at which point it transfers to her heirs. Her guardian is responsible for spending from this property on her needs and managing it through buying or selling for her benefit. Your need for the money does not permit its disposal. Any of her money spent after her interdiction is considered a debt upon the one who consumed it. If the grandmother passes away, the property becomes the inheritance of the heirs, and they may choose to forgive the debt.