Should a woman continue to secretly set aside money for Hajj on behalf of her mother, or should she involve her sisters in collecting money for Hajj on behalf of their mother?

It is permissible for women to share in the costs of Hajj on behalf of their mother, or for each of them to perform Hajj individually on her behalf. A condition for the pilgrim (who performs Hajj on behalf of another) is that they must have already performed their own obligatory Hajj. The heirs are not obligated to pay for the Hajj expenses of their deceased unless Hajj was obligatory upon the deceased and they did not perform it, in which case the debt of Hajj is settled from the inheritance before its distribution.