If she does follow the current plotline, we could either see the sleep-with-my-eyes-open strip or a rip-off of Dennis the Menace that has Mike wash Elly's typewriter in the kitchen sink.
I was right the first time; it's a Halloween strip from 1979.
Panel 1: We see a smiling Elly reading a pitcure book about Halloween to a regressed Lizzie.
Panel 2: We see Mike in close-up as he shows up and says "Hey, Ma! I finished digging out the pumpkin!"
Panel 3: As he stands there holding pumpkin innards and asking Elly where she wants him to put all the gucky stuff he's holding, we see that Elly is gobsmacked.
Summary: This is because she's forgotten that Mike is