I got to see the kids in their bathing suits whooping it up in the largish parking lot puddles as their mom shepherded them toward their minivan. They were enjoying themselves.
The woman in her new wellies must have gotten a similar thrill when she glided elegantly back to her car, impervious to wet feet and shoulders. She might have been too warm, but I'm pretty sure she was happy because she looked good and she knew it.
I got to wear an outfit that I liked, so that was good.
There really can be no rules for dressing in weather like this. The best you can do is just wear what makes you happy.