In the "Pilot" episode, Sara makes her first apearance. She arrives at the Heffernan house to tell Doug and Carrie that Tessie (Sara's mother and Arthur's third wife) died from a heart attack. At the funeral home she questions Carrie's decision to put Arthur in a retirement home, since she won't have a place to live, but Carrie insisted that she can stay with them, much to Arthur's chargin, who flatly insists that he can live fine by himself, but then accidentally burns his own house down with his "lucky" hot plate, he then has to move in with them along with Carrie's half-sister Sara. At the Heffernan House Doug was shaving but Sara runs in the bathroom and takes a shower while he shaves but Doug sees Sara's naked shadow in the shower and cuts himself a few times which made him late for work. Doug and Carrie then tell her to stop all this. It wasn't actually mentioned, but it can be assumed that after this episode Sara moved out of Doug and Carrie's House since she wasn't seen living in it after.
In the episode titled "Fat City" Doug meets Sara at Cooper's and mentions that Carrie has gained weight; Sara then insinuates that Carrie complained about Doug being unable to satisfy her sexually, and leaves abruptly.
- She is Carrie's sister but later on in the show Carrie is said to be an only child.