Affair Trade - S9-E2
Continuity mistake: When Doug and Jessica run into Carrie in the parking lot at the Dr. Heffernan office, there is a man walking up from behind them with grey hair. In the next shot he instantly appears beside them unrealistically fast. (00:19:20)
Answer: Sara hasn't been mentioned in later episodes, and it suggested in later episodes that she never existed, and that Carrie is an only child. Kevin James stated that the producers couldn't think of an good plots to use with Sara, so they left her out.