Thanks for all the virtual hugs and sympathy everyone. I appreciate it.
Just got back from the vet and... well, you guys are good! He asked pretty much exactly the same things as you all did. Of course, Windy came back with a clean bill of health - today. So in the end, we've decided to do nothing, not even a blood test for now. The vet said it likely wouldn't show anything anyway right now, since it was plain she was acting normal. The plan is, since her episode lasted for 2 hours and I am all of 10 minutes away from his office, if she has another episode I will whisk her off to get a blood test while the seizures are happening. That way we'll know if she is reacting to low blood sugar, thyroid issue, etc. right at that moment.
In answer to some of the questions here that the vet also asked, trying to find the "trigger":
Contacted the breeders: No epilepsy in their lines and they hadn't ever seen such an odd type of seizure anyway. Even if the breeders are fibbing, I would know since Shelties of this line are all over the agility courses here - four others just in my training club alone. I would have heard about it if these lines were prone to epilepsy. The breeders were very concerned about Windy, both have health guarantees.
Thyroid: Sire tested good, dam not tested. Windy if DEFINITELY not lethargic EVER - quite the opposite.
Blood Sugar: Except when she was very small, Windy has always been fed twice a day with quite a few treats in between because she is still being trained on a daily basis. Nothing was different Saturday.
Food: No food changes. She has always been fed Taste of the Wild Pacific Stream, a grain free food. Treats are either Zukes (also grain free) or plain cooked chicken breast.
Vaccinations: Not recently. She had her three parvo/distemper combos and one rabies, but that was many months ago.
Heartworm/Lyme: I live in a beach city section of Los Angeles. We really don't have heartworm or Lyme here - the vet never sees it unless it is a dog that has visited another area. I have had dogs all my life here and none have ever been treated for heartworm and none ever tested positive for it, even after hiking in the Sierras. Same with Lyme. Yep, I know about MDR1 - my Collie is mutant/non mutant (thank god she isn't a double mutant!)
Fleas: Windy has never been treated with Frontline/Advantage/etc. Yet, she has never had a flea - I flea comb her regularly just to check. My Collie started having reactions of those topical flea treatments, so I stopped using them. And I found a wonderful thing. In my neighborhood and also the place where I train obedience and agility (near Beverly Hills), people are generally well educated about dog care. They all keep their dogs on those flea treatments - which means my two dogs seem to reap the benefits in that they have no one to catch fleas from. My Collie has been without flea protection for over a year and I have yet to find even one flea on her.
Toxins: I don't spray my garden (in fact, the whole time I've had Windy I've been conducting a no-spray experiment with my roses, ditching those that can't cut it without spraying). The back lawn doesn't even get fertilized (it is all Bermuda grass anyway, which is nearly a weed here). My neighbors don't usually spray either, but there may be a possibility they did.
So.....
The only thing we can come up with that is different from the usual is that Windy just came in heat for the first time. It is "wait and see." If she goes without an episode until her next heat, we know what the trigger is and she will be spayed. Agility folks like to wait until they are full grown to be spayed, and she will be by then. She will likely be spayed anyway, as even with this one episode she is unlikely to be considered part of the breeding program anymore - in spite of everyone raving about her excellent structure and great drive.
