Original Commentary
If Kimberly is a pessimist and Brisbane is a optimist, what does that make Emily? Completely clueless.

Modern Commentary
Two: Emily recognizes that Kimberly has changed, and Brisbane is the most obvious sign of that change and is responsible for some of it.
You can't undo the past. Years of loneliness and living by her wits have changed Kimberly from the shy high-schooler that Emily knew to the emotionally-distant merchant that she is today.
Her friendship with Brisbane isn't the cause of that. It's her way forward to something else. But if you want things to go back to how they once were, then taking him out of the picture is the first step. - Terrence