Is it permissible for a daughter to finance her father's 'Umrah if he is not financially capable, so that he may be a mahram for her and her sisters, and would she be rewarded for it as an act of charity and for honoring her parents?

A daughter covering the expenses of her father's 'Umrah is considered an act of righteousness and good deeds for which she will be rewarded. It is permissible for a person to perform 'Umrah and Hajj with money donated to him by others, whether he is financially capable or not.