Marcia greets Molly and Col Whitfield at the front door and then, in her excitement, runs outside by mistake. No one locks the door (and it is not self-locking) but, once outside, Marcia knocks on the door and Col Whitfield opens it to let her in. The door was unlocked. It's unclear why Marcia didn't simply open the door herself.
Molly is running against Patty Hobert for banquet night hostess but in the scene in Marcia's bedroom before her makeover, Molly refers to her as Sally Hobert.