I apologize that my response might be considered off the topic, but it is in response to what I've been reading...
Wow...I've read this entire thread in one sitting and I eagerly await the next post, to know that all is well & is getting better.  I'm amazed at how well you, Becky G, have seemed to keep yourself together throughout all of this; then again, I'm sitting on the other side of a computer screen, not witnessing the emotional drain in the works.  I can empathize with you, though, as my cat Strasti (pictured, when he was a wee bit cranky) has been dealing with feline diabetes which took a turn for the worse a few weeks ago when he had a grand mal seizure (and his 4th seizure ever) -- he literally had no glucose showing up in his blood & he gave me nary a sign of going hypoglycemic (yes, he's been on insulin since March).  It was a torturous waiting game -- except, he had *a lot* of drs working on him for 3.5 days, and then it was up to me to get him eating again/stop vomiting, fight off his urinary infection & then maintain his glucose -- as he was off insulin.  I didn't sleep for a week, home-testing him at all hours & trying to get him to lap baby food from my hand.  Now,  3 weeks later, Strasti *seems* to be maintaining a healthy blood glucose on his own...but, we'll see.    
Like you, I did think of euthanizing him...it just wasn't right to see him suffer like that, and the physical toll on him was insane.  I really had to think about quality of life -- for him & for me.  But, I also thought -- like you -- that there was just too much life, too much of a spark left in him that I just couldn't give up on him yet.  He truly is my most expensive "possession" (if you can call a pet that), what with all we've gone through in addition to the diabetes in his almost 6 years, but he really is a trouper, also not unlike your Scarlett.  
I admire you for all of your efforts and optimism (though you may not feel like it's been there, it has...or Scarlett would not be thriving as well as she is!); it's so incredibly heartbreaking to deal with a sick animal, especially a beloved pet.  I wish for all of the best to happen for Scarlett & for you.  (You deserve some kind of pampering now!  

 )