The females are NOT automatically more dominent than the males. But they can be much more "bitchy" than the males and more into their own thing. You'll find more submissive females and more dominant males, just like in any breed. My male is pretty dominant and can be a big brat about it sometimes.
That breeder you're looking at is a pretty good one, I've heard of her before. However, bear in mind that her dogs are mostly old-school working lines, so they're going to be very drivey and harder to wear out than many others. Of course, they'll still have the brains an Aussie should and the easy to care for coat type, but you're REALLY going to have to have multiple outlets for them, otherwise they will redecorate your house on a regular basis.
If you want, tell me (or PM me) with what you're looking for in an Aussie and I'll see if I can't make some recommendations. The lines she has, Pincie Creek, Las Rocosa, Hangin' Tree (which feature heavily in Pincie Creek anyway) stay more in the working side of the Aussie while other lines like Briarbrook, Bayshore are the show dogs, which has it's own set of pros/cons.
If you really just want an Aussie b/c they rock and you want to get your feet wet and see if getting into sports/trialing or showing is something you're willing to go for, then start off with a rescue Aussie, see where your interests lie and then look for a breeder later.