I'm new to this game, and trying to figure things out. I have a good PEE KNN mare, and I'm trying to get her higher on the leaderboards, but when I look up the current #1 KNN CC Producer Mare, she doesn't even have any living foals, and does not show herself. How does this work?

Leaderboards work that way, that it counts 75% from the horse´s strength itselves and 25% from their foals.
You can not see how strong a horse is, because these are kind of "hidden points" only the game knows.

In this case I assume, that the mare is so strong herselves, that any foal might just turn her down the LB, or the foals just did not fit into that stable´s breeding programm so they were culled.

Ok thank you!