Is it permissible, in Islamic law, to disinherit a daughter if the cost of preparing her for marriage equals or exceeds her share, especially when there are other children, one of whom is ill and requires treatment?

Preparing a daughter for marriage is not obligatory upon the father, but rather upon the husband. However, if custom dictates that the father should assist his daughter, or if her marriage depends on it, then he should help her. What the father spends on his daughter for her preparation is considered a gift (hibah), not an obligatory expenditure. Therefore, he is not required to give his other children the same amount he gave her, because this preference was due to her need for marriage. Favoring some children due to need is permissible by Islamic law. The father does not have the right to bequeath a will preventing his daughter from inheriting; such a will is void. Every heir receives their rightful share regardless of the amount of financial support they received.