When someone overreacts in front of an annoying situation, our first instinct is to think, "What is wrong with them? It's not such a big deal," and usually, it isn't really such a big deal. I can assure you, I've been on the overreacting side more than once, and it's never just about that specific moment. That situation that sends us spiraling is the last straw in a pile of things that have been bothering us for a while, but we haven't had the time, tools, or occasion to solve.
Something similar happened to this woman, who was absolutely on the verge of losing it against her mother-in-law for overstepping her boundaries.