Is training "included" as part of the boarding package with your horse, or is she just some trainer who happens to use that barn to give lessons out of?
If you don't like her training style, and your boarding fees do not include training time. . .make it clear that you are only there to board and you are not interested in her training services, or "help" from her in any way.
It's your horse. Unless you're paying her for her "expertise," she needs to mind her own business and stay out of yours.
If your boarding package includes training. . .see if they offer a package that is ONLY board. Make sure the BO/BM is aware that the "trainer" does not have your permission to work with your horse. Put it in writing, too, and date it, and make sure it is clearly understood by them and the rest of the staff.