I've been reading though all of this, and I'm so sorry that you're having to deal with this! I'm so sorry for your poor adorable bun.
I don't have much to add, other than my bun and I are sending good thoughts to you and yours.
I don't know anything about treating head tilt or anything you're dealing with. But I know when other animals take steroids and when people take steroids, it causes increased thirst. I don't know if your vet told you that(she probably did) but, thats something to keep in mind, if the same applies to bunnies(it may not)
I think that you're doing the absolute best you can do for your poor little bun. Keep up the good work and the kind heart. Again, my thoughts and best wishes are with you!