Praise be to Allah.
The way things were was done at the time of the Prophet (peace and blessings of Allaah be upon him) and the Rightly-Guided Khaleefahs (may Allaah be pleased with them) was: when a woman died, she would be washed by other women, not by men, except in the case of a wife whose husband could wash her or leave it to the women. The same applied to a slave woman in relation to her master, so long as she was permissible for him. If a man died, he would be washed by other men, not women, except in the case of a husband, whose wife could wash him, or leave that to the men. Based on this, your doing ghusl for your mother is contrary to sharee’ah, because of what is known from the Prophet (peace and blessings of Allaah be upon him) and his companions (may Allaah be pleased with him), even if your mother was old. You have to seek Allaah’s forgiveness and repent to him, and not do anything like this with any of your other mahrams, even if your intention is good and you want to honour them.
And Allaah is the Source of strength. May Allaah bless our Prophet Muhammad and his family andcompanions.