Is it permissible for a girl who has passed away and was not married, to bequeath her money and possessions (gold, money) to someone before her death, or how should they be disposed of?

A Muslim's bequest of a portion of their wealth (one-third or less) for the purpose of seeking nearness to Allah and earning reward is commendable. There is no difference in this regard between a rational person, an improvident person, or a heedless person. Therefore, a girl's bequest of a portion of her wealth (whether gold or monetary amounts) is considered a charitable act for which the doer can hope for reward from Allah.