Is Zakat obligatory on a girl if her bank balance reaches the Nisab, and is it permissible to deposit Zakat funds into her account to help her with her marriage?

If a girl is in need, it is permissible to give her from Zakat (definition) only to the extent of her basic needs, and not for saving for marriage. However, it is permissible to give her [from Zakat] at the time of her marriage if she is in need then. Whoever's wealth reaches the nisab (definition) (minimum threshold) for Zakat and a hawl (full lunar year) passes on it, Zakat becomes obligatory upon him. It is not permissible to deposit money in an interest-based bank, even if no interest is taken from it, because it constitutes cooperation in sin. It should be deposited in an Islamic bank, or kept at home, or with a trustworthy person.