I would love to claim that I made Jay smaller to set this up, but nah. I just thought it would be funny if Susan made Jay smaller than herself.
It was only after that decision that I considered the various problems with that and solutions to those problems. It was fun.
As for why the heck Jay did that to her shirt, I sketched panel three first, and the default top looked really bland, so... Yeah. How this makes ANY sense in context, your guess is as good as mine.