Horse who's afraid of horse trailers!!!?

There's a horse I ride quite often who is the sweetest thing alive until she sees a horse trailer. She totally freaks out even if you're juz walking past the trailer and starts backing up. At one stage she had to go to the vet and freaked out so much she ended up hurting her hindleg. She's obviously scared of loading because she probably had a bad experience in the past so I have to take a pive, non-forceful route to helping her. So pls if there r any horsey people out there with experience pls give suggestions.