Susie's Mother is the parent of Susie Derkins . She was seen in one strip from the waist down (resembling Calvin's mother). She also was referenced by Susie in another strip.
Calvin meets Susie's mother.
Her mother also appears off-panel when Susie goes to Calvin's house to ask for eggs for what looks like a tea party and she asks if they gave her eggs, but Susie, meeting Stupendous Man, said no one was home. And in yet another she called Calvin's Mom because Calvin dropped a snowball on her head from the top of a tree as Stupendous Man. She appeared yet again when Calvin was trying to smash Susie with a giant snowball. When he was caught, he quickly says he is selling the snowballs, then commenting later that his "Plan B"s leave a lot to be disired.