Usually we have both girls in the room and they take turns with the shots. We used to have Clara go first because she got so upset and then Walt would take her out of the building (usually screaming). Lucy would always be upset at the start of her shots and we'd inevitably be leaving the office with two screaming babies.
This time we tried separating them. W waited first in the room with Clara while I waited with an undressed and ready Lucy in the hallway. W said Clara didn't even cry for the first shot, but he took her down the hallway crying as I went in the room. Lucy didn't cry for her first 2 shots and she calmed down very quickly.
Since I didn't hear Clara screaming I assumed W had taken her to the car. Instead, as I walked down the hallway to checkout I saw him there holding Clara with a piece of paper in his hands. Not only was Clara calm, but he had also checked us out and scheduled their next appointment.
I really wish I had figured this out sooner. The girls were obviously feeding off of each other and making themselves much more upset. Even though the majority of their shots are done, I'm still planning to use this tactic for any further appointments.