You were wrong to act like that. IMO it is none of your business how she trains your horse, or wether you agree with it, unless she is beating it, its none of your business. If you didnt want to ride her horse anymore then say you don't want to, you don't need to go on with everything that's wrong with him, that puts ANYONE in defence mode, if someone insulted my horse like that I would probably reply a lot meaner then she did.
It is not your job to tell people what theyre doing wrong, or how well they ride, that's your trainers job.
In all, to me you sound like a teenage girl with a tampon up her butt. Haha not the nicest way to put it, but we all have those kinds of moments.
I don't know all your background information with her, but to me you were beign very rude acting like that, and it seemed like you were looking for drama. If I were you I would go back and say sorry for acting like that.
If there are no horses in heaven... im not going.