Is it permissible for a mother to give her daughter a sum of money to celebrate her success in general secondary education, and would that be considered unfair to the rest of the children?

Parents must be just among their children in giving, and it is not permissible to favor some children over others in giving except for a legitimate reason, such as helping with marriage, or covering the expenses of medical treatment, or as a reward for academic success or memorizing the Quran. In this case, they are not obliged to give the others a similar gift. However, if the same reason recurs with another child, they must give to whoever meets the same condition.