Panel 1: We find ourselves at the "Let's Dump All Over Baskin Robbins" stand as Mike orders a cone for himself. As he does so, Liz tells him that she sees Martha over in the distance.
Panel 2: We then see Liz prove that she's never going to understand social norms when she says that Martha is probably sorry that she dumped a boring git who treated her like garbage when he wasn't ignoring her for months on end and besides, who needs a girlfriend when he can be seen having to indulge the need of Baby Sister to be carried around in a sedan chair like this is Czarist Fucking Russia?
Panel 3: Liz doubles down on being too stupid to function in society when she can't see Mike importuning her to do him a solid coming.
Panel 4: This is why she's devastated when he tells her to sponge it up and disappear for a bit.
Summary: Liz really is stupid if she thinks that a normal boy is going to reject a chance to try (and fail) to make his case in order to hang out with Tagalong Kid Sister. She's a stupid as her father when he was baffled by her wanting real friends instead of a dog, parents who ignore her and a big brother who'd really like it if she would apologize for invading his home and making him do things he doesn't want to do before going away forever.