Can prayers be made up for a deceased mother who was remiss in her prayers due to an illness that led to involuntary urination, and what can be done to alleviate the distress of the grave for her and add good deeds to her?

We ask Allah to forgive your mother, have mercy on her, grant her well-being, and pardon her. As for what she was unable to fulfill regarding the conditions and pillars of prayer, those obligations are waived for her. The prayers she missed are not to be made up on her behalf. However, you should frequently supplicate and seek forgiveness for her, or perform any act of worship and dedicate its reward to her, as that will benefit her.