That fun police attitude is quite common in a lot of herding breeds, kind of goes along with the whole herding instinct thing. I tend to see it more in girls than boys, so that's something to consider as well.
Koolies are a great option, they tend to be more on the higher side of the energy spectrum but from what you do currently, should be just fine. They do tend to be more vocal than the other breeds you mentioned so that is something to consider.
Aussie would be a good choice, they tend to be more even-keel in temperament and could be a nice rock for Zelda to rely on. Some do tend to be snarky to other dogs so make sure to research lines and you should be good to go!