Snake Bit--Again

So, yesterday around 10 am, the fog had broken up & the sun was shining and the flies were waking up and it was time to get the horses dressed w/their fly masks. All the horses were just fine. Around 2 pm, I went out to clean & refill a water tub. Sedona, the TWH mare, parked herself behind me and demanded attention. I turned around and did a double take; I knew what I was seeing but just could not believe it. Immediately behind the corner of her mouth was a big, rubbed raw wound with swelling. The swelling was hard as a rock. The wound had two points of origin. I was looking at a rattlesnake bite.
The wacked part of it? This same horse got bit in the same place 2 years ago.
I looked at her; "Geez mare, didn't you learn from the first snake encounter?!" "You have now proven that my cats are smarter then you." (cat vs. snake is a story for another time)
I trekked down to the tack room and got Betadine solution, gauze, providine ointment and horse cookies. Don't need a halter; as long as I have cookies or carrot slices, she stands for all necessary treatment just fine. Back up the hill to sort her out from the other 2 horses so they don't chase her off for the cookies. Yep, there are indeed 2 points of main damage, one of them a nice deep pit of already dead flesh. As I am cleaning off the smeared blood, I note that it looks like she has another set of fang marks on her chin. I call over Senior Handyman and he makes the same observation.
I put in an emergency call to my vet who returns my call promptly and we discuss what to do. Turns out he is getting ready to leave on vacation and he took my call because he recognized my phone number. The word is to start her on Bute or Banamine (I chose bute because it is cheaper) and antibiotics. He knows I already know about cleaning it for as long as it takes to heal and what to watch for that may need a vet visit.
When I go to give her the bute, the swelling has increased but continues to be very localized around the corner of her mouth. Same as last time, her head does not swell up. The vet said two years ago that some horses seem to contain the venom near the injection site while others spread it and have more problems.
Three hours later, the swelling has either stopped or gotten so slow that I can't see the increase and she has stopped rubbing it. I will attribute those to the bute but have no proof of it being so. She is happy to eat dinner and her soaked hay pellets with oats and SMZ.
This morning the swelling has stabilized and she has refrained from further rubbing. She enjoys the cleaning w/betadine, with cookies. She enjoys getting the SMZ, with soaked feed. But she hates the syringe of bute. Oh well, 2 out of 3 ain't bad!
If this is like before, we are in for a lot of tissue sloughing as the venom kills flesh further from the injection site which means lots of cleaning to keep the necrotic tissue from causing infection and to keep the fly eggs out. The location prohibits any true cleanliness and of course wrapping/covering. The best I can do is to cannibalize a piece of mesh off an old fly mask and use a diaper pin to pin it to her mask to hang down over the side of her mouth. It does keep off a surprising number of flies. Last time, which had less swelling and a smaller initial wound, it took a month of daily cleaning and another month of sporadic cleaning to fully heal.
Really, mare, AGAIN?!