My first horse did this. He did like to go for rides...it wasn't that he didn't want to leave the barn. But when he didn't want to do something, he'd start backing, backing, backing, right down ditches, down hills, over lumpy ground, up against a log that might be down, which could have caused him to fall..... it was dangerous and
very maddening.
I was a young teen then...like 12 or 13 and had been riding for a few years before that, but hadn't had my own horse before. He came like that as a new horse. He was broken to ride, but nothing more, not neck rein trained, didn't know leads, couldn't canter without trotting for a million miles first..no training other than they must have taught him to back up.
Bad idea for a first "trick."
Anyhow, it was a bad feeling when he would do this and I wasn't going to stand for it. I
really let him have it. Kicked the livin' daylights out of his sides, bam, bam, bam, bam, bam, slapped the reins back and forth from one side of his butt to the other very fast and very hard. And hollered at him, "
Git up there!!!! Move your bloomin' arse!!!" He got over it. I don't recommend you do that though.
Meanwhile, I taught him other things...lots of other things and he got rewarded with carrots and praise. He was interested and busy learning new things and he lost interest in doing all that refusing and then backing. He eventually learned to back up correctly,
when asked, side pass across a log, learned collection, leads, flying changes, and leg yields etc, etc. I never had to get after him or be rough with him again. He became my show horse. But that first few weeks of having him was a challenge.
Horses are a whole nuther ball game from dogs. You can
not let them think you're wishy washy. Once they get your number, your screwed. If you're not familiar enough with horses, I strongly recommend getting a reputable trainer (one that doesn't do what I did) to help you. The one thing though...you can't equate slapping a horse with slapping a dog. No, you don't want to make them fearful of you and some horses are softer than others. (mine was as tough as nails and not one bit flighty) I wouldn't
never have done that to my Arabians and I suspect not to a Thoroughbred. They're too flighty and sensitive and no telling what would have happened to them and me.
I have no doubt that positive reinforcement would work well, at least for most things. But you can not compare a horse and dog. Dogs are so very intertwined with humans in their evolution. As far as I've discovered in having horses most of my life, you do need to show them who's boss. You don't have to be smacking them around and shutting their spirit down. But you can not be indecisive one little bit. They are the epitome of give and inch, they'll take a mile. I think they invented that.
Ps....what you did, a little kicking/slapping with reins, I doubt very highly, did a thing to your horse. Like BB said, there can be lots of things going on, lots of factors that we couldn't possibly know. So therefore, it's vital to get a professional trainer to help you. Or sell this horse and get an easier horse. Don't let emotions make you keep a horse that isn't right for you. There's no shame in selling her to someone who is more accustom to working with this. Sometimes it's worth spending the extra dough and getting yourself a horse that has some good training on him/her. (a middle aged gelding might be a better choice than a mare) jmo....not tending to be as flighty.