Which sentence from the following the conversation most clearly illustrates the technique of outlining a discussion plan

I would say that the sentence from this conversation (that you forgot to include here) that most clearly illustrates the technique of outlining a discussion plan is the following one:

A. Why don't we start with the symbolism of the door?

This sentence shows us that Jennifer thought about how she would start this discussion, which is obvious if you take a look at the sentences following that one. Her plan is to start with the symbolism of the door, and then move on to other moments in the story.