My tiel, Snuggles, seizes every time we step into the vet's building. And that's even with a cover on his cage to try to calm him/conceal him seeing the building before he goes in. He even seized once at home when he became upset about having to come out of his cage to go to the vet. I backed off, waited a few minutes and he stepped up just fine.
Thankfully, he comes out of the seizure just fine and does not require meds. I know the terror and helplessness you must feel. I wish I had the answer for you. I would try to get someone to the house. Do you know of a vet technician who could draw blood? Only my vet draws blood. I don't know if techs ever do.
I would beg the vet to make an exception. If he refuses, I'd ask him if he knows anybody. If you're on other bird boards and have bird friends, ask them. If you know of reputable bird stores or breeders, ask them. If you belong to a bird club or foundation, ask them. Keep digging.
Lafeber makes is something called Medi-berry, which is basically a Nutriberry with space to put meds.
I don't like the thought of sedatives. I have never used them, and for all I know, they might work, but that would be my very last resort. If your vet won't come out, ask him what you should do when your baby does have a seizure. Ask him to teach you what to do. Also, research why birds go into seizures and prepare as best as a layman can when it happens.
I wish you and your girl the very best of luck.
You were clever enough to give the bird some Karo. That tells me you can handle this! You can. You can do it.