There was a strip to this effect when Liz was about ten, only in that case, she was doing it to Farley. And she was inspired by a TV show in which some nutritionist or something suggested making mealtime an adventure, so she blindfolded Farley and pulled his dish around on a string to see if he'd follow it. She wasn't torturing him, mind, and in fact, we didn't see a reaction from him other than "?"
As for this strip, I still don't see how this could be Liz's memory. Elly's actions in the last panel are ambiguous: is she taking him away to punish him, or is she just removing him from the situation by force? Notice Elly's long stride. That was an LJ trademark in the early years. Perhaps that's why Elly started gaining weight: she stopped expending so much energy and burned fewer calories.