LW sounds like they've somehow had some trauma triggered on this issue. It reminds me of a couple of incidents I've witnessed where a friend in one case, and my mom in the other, got crying, ranting, obsessively upset about relatively innocuous and incomprehensible things that were surprising and confounding to all the witnesses (some random friends in one case, my mom's siblings and children in the other). I observed the same pattern both times too, of them getting further upset because of the people questioning them to try to figure out what was upsetting about it - the suspicion of gaslighting, because they apparently couldn't conceive that the trigger wasn't so obviously wrong to everybody else.

I've been trying to tell my mom and dad that she definitely needs therapy for whatever that was for several years now, but of course she still doesn't believe her reaction was odd - she thinks every other person aware of the situation was wrong.