Dogs rule, people suck.
I have been in similar situations up to the crazy lady screaming suddenly appearing to gather her dog, but no way in hell close to what you dealt with after that point. I am honestly and without any bs jaw-drop impressed with your restraint. I have very little confidence that I would have shown even half of the good judgment you did. Thumbs up, bigtime.
To do differently next time.... hmmmm.... well, I often carry the little "HALT!" mace canisters that are marketed for bike riders and so on, and I have maced dogs that would not back off my dog(s). I hate doing it - would much rather cause pain to their idiot owner - but I have - right into their muzzle. They aggression, in my experience, is gone instantly. You are right, imho, that calling your dog when they were locked-up in posture probably gave the other dog just the motivation to attack, but at the same time I would never fault you for that. You know your dog will recall, your dog is reliable, and you are not (yet) within grabbing distance. Seems like a natural reaction to me.
If you wanted, you might have filed a police report of the incident just to be the 1st reporter, or perhaps write an account of the incident and seal a copy in your safe or something just in case.
One thing to keep in mind is that as you are pulling your own dog out of a fight, even IF your own dog doesn't spin and nail you (not their fault at all - instinct to expect another member of a pack to join in) the dog they are fighting very well may come after YOU. A dog the size you described ... dangerous dog. Very much so. Her dog could very well have ended up shot dead in such a circumstance, and the shooter with a torn open thigh/arm/belly to show for it.
Breaking up a dog fight, the best way I know is to have at least as many humans as dogs, everyone grab a tail and run backwards. Preferably the tail of your own dog so when/if they spin and nail you, you are only mad at your own dog. Unfortunately, I have had very few experiences of separating a dog fight by myself that did not result in me bleeding from somewhere. Catch poles work to a point, that point being you have one dog under control now but the other increases its intensity... lather, rinse, repeat.
They're critters. They're dogs. I get beside myself annoyed when people blame dogs for being... dogs.
I am not even going to approach the part of her planning to mace you while you are in your own vehicle attempting to retreat.... I would say something offensive, I am sure. See? Already you taught me some restraint!
Good job.
~tracy