If it were EYP then likely antibiotics would be needed, I don't think it likely that the infection would clear up on it's own. If it only happened once, and cleared up I would be more inclined to suspect a glitch in the system, which can be caused by all sorts of things like stress (which encompasses a pretty broad range of causes), going in and out of lay, etc. Sometimes that happens and the cause is never known, if it's a one time thing then it may not be anything to worry about. If she seems fine now, I would just keep an eye on her and if you see any signs of illness then follow up right away.
Hens go broody when you don’t want them to… and won’t go broody when you do. 