Barbara McFarland

At least four of the seven flight attendants who will be on United Airlines Flight 175—the second plane to hit the World Trade Center—on 9/11 are not originally supposed to take this flight, and are only assigned to be on it shortly before September 11:
Amy Jarret will be on Flight 175 because she switches shifts with one of the original attendants, Elaine Lawrence. [San Francisco Chronicle, 10/23/2001]
Robert Fangman takes the place of attendant Elise O’Kane, who accidentally enters an incorrect code into the computer when signing up for flights, and is instead scheduled for flights to Denver during September 2001. [Boston Globe, 5/22/2005; CNN, 10/8/2005]
Lauren Gurskis reschedules herself to a September 12 flight so she can drive her son to his first day of kindergarten. Kathryn Laborie is most likely the attendant who takes her place. [Boston Globe, 9/8/2002]
Barbara McFarland swaps shifts with another attendant so she can spend an extra day with her son. The attendant that replaces her is unstated. [Cape Cod Times, 9/14/2001; Cape Cod Times, 3/10/2002]
Many of the flight attendants who will be on the other three hijacked planes are also only assigned to those flights shortly before 9/11 (see Shortly Before September 11, 2001-Early Morning September 11, 2001, Shortly Before September 11, 2001-Early Morning September 11, 2001, and Shortly Before September 11, 2001).