It might have been the white sides, which are not normally found in most barns. Or, she could be one of those (and I have two of them) who just do not like to be stalled. You could try music – play it at home and at shows, so there is something familiar to her. Another possibility (might be difficult to do) is to take her somewhere, put her in a stall, but only for a short time and then bring her back home. Does she have a favorite companion? One who could accompany her (a goat would be better than another horse, as a goat could stay in her stall). Of course, the goat thing could lead to other problems, if you had to take her somewhere without it. It might also be that the few months you have had her just aren’t enough to build complete confidence that she won’t be abandoned, and time might cure that. Good luck, and let us know how she does.
It is never the horse's fault