As far as your mare, I would definitely do short trailer rides until she is relaxed...and start out without even going anywhere. Load her, close the door, and unload. Etc... I would say even incorporate methods that encourage her to WANT to be in the trailer. Ie, work her around the trailer, and ask her to load, then take her back out, and do some more work. When she is comfortable self loading, and standing there calmly, then start tying, closing door, etc... It WILL take time, but I think this is something you can eventually get her over...be patient, and consistent with what you are asking, and how much you ask of her each time.