Liz has acquired a terrible, disfiguring illness. Witness--
Panel 1: Liz has a very square-ish figure, almost without hips or boobs.
Panel 2: Liz has suddenly sprouted oversized and sagging shoulders and a rather large sagging bosom. Maybe the disease is called Large-Saggers Syndrome?
Panel 3: Liz is suddenly a giantess. A giantess who looks exactly like her brother Mike wearing a bun. Her nose has swelled up greatly, and the tip is sagging abnormally low, almost to her upper lip. Yup, it's definitely the dreaded Large-Saggers. We knew Elly was afflicted, but it's sad to see it in one so young.
Panel 4: Liz is now her usual height, but her entire body is swollen and puffy, as if she is on high doses of steroids. Her face is much like it was in yesterday's last panel, though, except then it was emaciated. I'm now thinking this style looks more like a Fisher-Price Little Person than a Muppet. Same saucer-like eyes--or they would be, if her cheeks weren't so puffed up.
I'm guessing that when she saw the first signs of Large-Saggers manifesting itself in her visage, she decided to run away and pre-empt Paul from the inevitable dumping that would occur when he saw she was turning into a hideous physical ruin, just like her mother.
As for the dialogue: I'm not sure Lynn is capable of doing a storyline that doesn't include some kind of poop joke.