Has the daughter fulfilled her mother's debt when she donated an unknown, estimated sum of her own money with the intention of paying off the debt, and then paid off another debt on behalf of her mother from the latter's inheritance?

The sister who asked the question is obliged to repent and feel remorse for what she has done, and to return the unlawfully acquired money to the heirs of her deceased mother according to their rightful shares. She is permitted to take her own rightful share as one of the heirs. It is not sufficient for her to give the money to her aunt; rather, she must retrieve it from her and inform her that it is a right of the heirs. She is not obligated to inform them how she acquired the money from her mother.