I'm reminded of something I saw on "Facts of Life"; for some reason or another, Mrs Garrett was getting on Tootie's case because the young lady decided to wear leg-warmers of a morning. Rather than assume that the younger person simply adopted a trend or wanted warm legs, the old doll clearly seemed to think that the black kid in the roller skates was man-hungry and trying to draw male attention. The same impulse inspired Elly's hostility and panic when confronted with the scary sight of Martha wearing a tube top and bike shorts while roller skating. I know that I've talked about the whole fashion cop thing that the Pattersons do and why it's inspired by the fear that people will judge them by what they let the kids wear but the need to protect them from the scary outside world is only part of it.
What I think is happening is that while Elly fears and hates having her husband stolen away from her by some busty something in a magenta leotard, she hates it that she's no longer leotard compatible. Ah, well. At least jealousy and self-loathing are less irritating than blind panic and fear that his children will disgrace him; this is why John (who's gone on record as saying that April will inevitably go on porn sites and communicate with hate groups because network television says so) plays fashion cop because of that whole Mrs Garrett deal I talked about earlier.