That being said, I also hinted at another factor: her fear of knowing what she really looks like. First off, she tends to think that she's older, uglier and fatter than she actually is. This is best highlighted in this strip wherein Elly celebrates turning thirty-five by not wanting to really accept being old and undesirable and fat and ugly and a lot of other things she ain't. The voice she wants to hear tells her "Face it, Elly....the glory days of your youth are loooooong gone and that's sooooo unfair!!" Exposure to home movies would force her to listen to the voice she doesn't want to hear. The voice she doesn't want to hear says unhelpful things like "John is right, STUPID!! You'd look and feel better if you didn't slouch over like you've got the weight of the world on your shoulders! Stop playing the victim all the time and be grateful for once, DAMN IT!!!"
Another reason she doesn't like watching home movies is that they make her see what her children see: a dull-witted nag who storms over and just plain starts bellowing at children for what they didn't actually do. She has this image in her head of herself being loving, fair, firm, kind, understanding and sweet-natured BUT misunderstood by children who, because they love chaos, force her to act out of character. Watching herself in action tends to do something unpleasant by making her see a testy, distant, arbitrary, short-tempered and intolerant blowhard who swoops down at random and bellows at children because she's too stupid and stubborn to get her facts straight and too vain to admit that people aren't trying to eat her brain.