I think any salt is fine. I have done sea salt myself. Never done epsom, but I don't see why that wouldn't work. I think you want it a little saltier than saline solution, but I am not super familiar with the usual concentration in saline solution. You can use that in a pinch, like if you need...
I'm not 100% but I thought that terramycin was sold at feed stores. You can also try just doing warm salt water soaks if it is just injured.
Does she have calm friend that could potentially be in the crate with her? Or maybe let her run with the flock, and then treat her at night when she is on...