Any respiratory infection can come with a high fever--flu, rhino, EVA...it doesn't have to be strangles to have a high fever. The banamine was a good treatment, but it's too bad you cannot get some antibiotics. antibiotics, of course, won't help with a virus, but they will ward off a secondary bacterial infection, and if it happens to be bacterial and not viral then it will help.
At the first sign of a foal being off its feed we start giving antibiotics. I'm not big on penicillin, for two reasons--I dislike having to inject the stuff, and more importantly I haven't found it to be particularly effective for the respiratory infections we've had here. I much prefer the oral Uniprim, and when that doesn't work I use Excenel. With older horses I will take a wait and see approach, but not with the foals.
I'd think you can buy penicillin from your feed store? We can here--it's not a prescription so we don't have to buy it from a veterinarian. The Uniprim and Excenel do have to come from the vet, and I am sure glad that we have vets who will give us those medications on request. Is there another vet some distance further away that you can go to. Depending what "bug" your baby has you may be needing something more than just the banamine.
Let's hope, though, that this is just a viral thing that will run its course very quickly, and your foal will be feeling better again real soon. How is she doing tonight?