(Strip Number, Original Publication Date, 10 October 1988)
Panel 1: We find Elly making Lizzie's lunch for the day only to have the child object because she's making the cheese sandwiches that she hates. For once, we get the bone-weary sigh one should expect when Irritated Elly mutters "Fine."
Panel 2: She then does something Lizzie neither expected nor particularly likes when she says that since she's big enough to make her own lunch, she should do so.
Panel 3: As Elly puts her next to the counter, she sputters "But, but...." because she wanted to make Elly make something else instead of having to make something else herself.
Panel 4: Mike does nothing for Lizzie's mood when he says "Say cheese" in order to somehow hang a lampshade on how she'd talked herself into this.
Summary: This is part of what I like to call a barometer arc. This is because Aaron and Katie probably used to follow the strip in order to know what Mom was mad about six weeks earlier. Judging from this, it would appear that she was angry because they expected her to exit her fantasy capsule and interact with them as if she were their mother or something.