(Strip Number 6049, Original Publication Date, 29 December 1988)
Panel 1: As she looks out the window at Mike, Bev tells Elly that she doesn't think that he's having an especially good time. Elly, who's as attentive to her son's needs as ever, tells her to not be silly. After all, once he cools off, he'll remember that he can never allow himself to complain TO someone who can fight back.
Panel 2: When Bev alludes to the plumbing problems they've had and the fact that Carrie's need for quiet in the mornings has cast a pall over the fun-filled fun when pointing out how hard it is being a guest in someone else's house, Elly tells her that things are really fine.
Panel 3: When Bev points out that it's hard sleeping in someone else's bed (or in a hallway to get trod on by inconsiderate little finks who have it in their empty heads that Mike chose to sleep there to make her life worse, LAURA!!!) and that the kitchen's small, Elly tells her to not worry about it. Bev is about to say that she realizes something else that Elly didn't foresee, she doesn't quite get there.
Panel 4: This is because having to deal with all that hindsight causes Elly to angrily yell that they're having a wonderful time. Bev is taken aback because she either doesn't realize that Elly is trying to save her from the humiliation of admitting that she and her family haven't been very good hosts or that her sister-in-law has it in her head that she can't allow people who are mistreating her to feel bad about it.
Summary: The obvious conclusion is that Elly knows that the family isn't having a wonderful time and wants to save face so as to avoid admitting that she half-assed her way into another disaster. Tune in tomorrow when John trolls her mercilessly by proxy.