Is it permissible to give money to a daughter to secure her future, even though she is 31 years old and there is an employed son?

Justice must be observed in gifts between children, male and female, unless one of the children has a legally recognized need that necessitates favoring him. In such a case, it is permissible to single him out with a gift, and this is not considered injustice. If there is no such need, then equality between them is obligatory. It is narrated from Imam Ahmad that it is permissible to single out one of the children if he has a need, or an infirmity, or a large family, or if he is engaged in seeking knowledge, or if the other is a transgressor (fasiq) or an innovator (mubtadi').