Close; it's a strip from October 1979 that depicts Elly using the Penetrating Glare of Hostility to force the truth out of Michael.
Panel 1: We start out Elly staring down a filthy Mike as he stammers "I wasn't doin' anythin'...much...well....Lawrence was walkin' the fence. An' there was this big puddle, an', an'..."
Panel 2: As she continues to stare him down, he hangs his head and says "He sort of fell off...er...I sort of helped him fall off...an'...well...he put a gob of mud on my head..."
Panel 3: She kneels down, grabs him by the arms and looks him right in the eye as he says "...So...well...I sort of put a gob of mud on his head...an' he told his Mom...an' his Mom yelled a whole bunch...an' then I came home."
Panel 4: As she marches a scared-sick Mike down the hallway while grabbing him by the shirt-collar in a triumph that has done a number on her proportions, Elly thought-bubbles "Yessir...they can't escape the ol'stare-of-truth."
Summary: Upon seeing this example of crappy parenting that had Elly pat herself on the back for reminding Mike that she has no forgiveness in her, I felt as sorry for Mike as I do for all the readers who have to contend with plot-induced whiplash. As aprilp_katje said, Lynn seems hell-bent on using up every unrelated first-year strip she can wedge into continuity. It doesn't matter that this depicted a much younger Mike than we saw yesterday; all that matters is that it reminds us that Lynn is convinced parents and children are natural enemies. What a wondrous victory she has encompassed today; let us mark how glorious it is that she terrified a small child for her own amusement over a total non-event.