ok but since Shirley was the one that actually went and arranged the room swapping amongst all the people involved, and the first person she goes explain it to was Jo.

like imagine Jo hearing Shirley explain to her this extremely convoluted three way swap that is necessary because Jo's perfume will trigger her allergies, they don't want to offend Jess, and they have to keep up the spirit of collegiality, meanwhile Jo probably doesn't even wear any strongly scented thing at all and so she's just sitting there while Shirley explains this until Shirley ends with the fact that Carson and Greta would be rooming together