I know the type of barking you are referring to and I think that is the worst type to have to deal with. I'm thinking that if she could become more acquainted with the horses - up close, that might be of some help, but with her being in the state that she is in, I don't know how you would attempt that. Right now they are something different and unusual invading her surroundings. There may be a possibility that she will eventually get used to them being there and this behavior will diminish.