Hm, I always thought her Patronus was an otter because they were clever and JKR's favourite animal is an otter...but I suppose the Ron thing makes sense too.

I like the idea of a dolphin a lot, actually, and it's a water animal, like an otter.
What about some sort of cat, maybe not like an Umbridge cat, but like a wild cat, like a cougar, or maybe a lioness.