Is it permissible for an unmarried girl who is financially capable to pay off her father's accumulated debts with her Zakat money, knowing that she does not have a fixed income, spends on herself, and her family does not support her? And is she obligated to spend on her well-off family members who are extravagant in their spending?

For zakat (definition) to be due, a full year must have passed on the wealth that has reached the nisab (definition). It is permissible to disburse zakat to pay off a father's debt if he is in hardship, and he is not required to repay the debt. However, it is not permissible to give him zakat for his poverty, because his maintenance is obligatory upon his son. Similarly, the maintenance of parents is not obligatory upon the son as long as they are not in need, but it is commendable to give them money to please them.