Peggy Gallagher, Frank’s biological mother, is a character that makes a certain impression despite only appearing in a few episodes. Briefly seen in the first season, she takes on a larger role in the second season after her release from prison. It is here that she finally meets Debbie, Carl and Liam, who are all a little taken aback by her. During this arc, Peggy bribes her grandchildren with various gifts and even opens a meth lab with Carl. Sheila, currently in an odd relationship with Frank, quickly develops a strong dislike for Peggy due to her constant disrespect.
At some point, their mutual dislike reaches such a climax that Peggy fires a pistol at Sheila in her own house. Afterwards, Frank and Fiona find out that Peggy didn’t stay long in this world due to a legitimate cancer diagnosis. Not wanting to prolong her own suffering, Peggy gets along with Sheila and allows her to kick her. Sheila then decides to suffocate her with a pillow using her entire body weight, which finally sends Granny Gallagher to the pearly gates. This, of course, is a huge relief for Frank, who is finally free from his abusive mother. He even welcomes her passing.