...However, I think I ran into a huge trouble with her the longer our session lasted.
She has been worked in a way that she gets a click for reward as well as "loose" (removal of pressure). Either one on their own should be ok. Usually after a series of clicks, a treat. Well I didn't have any treats with me, so I mainly let her stand and took away the pressure as a reward. A click here and there, but as I'm not a clicker training person, it doesn't come naturally. She didn't see petting as a reward (tried).
These are the problems I see: thinking of the horse in a sort of mechanical) or computerized?) way, that you do something, and you should get the same result. Every time. You push a button, the thing happens.
But horses are living creatures, living in an ever-changing world. The "session" changes as time goes on. The situtation after ten minutes is not the same as when you first start out. What makes it different?
The second problem is along the same lines, the concept of "reward"--do horses even think of it in our terms? I don't think so.
To me it's one of the most fascinating things about the human-equine relationship. We see in a narrow focus, through time; horses see nearly everything in a globe around them, in a compressed, strongly (but not absolutely) now-time. We expect food to be a "reward" because to us, predators, it is. Horses more or less expect food to be around them at all times. They graze and browse.
So what is this "reward"? I believe it's a shift in the whole circle of their now-environment: a time for pause, to taste and move the tongue, maybe to look around. They like the taste of the sweet; but we've all had horses who wouldn't take a treat. It's not a guaranteed reward.
I've been trying to work out WHY any of our training even works. I'm beginning to think it's because horses in general ENJOY the break, or mark, or poke, in their awareness; just the way we (or I, anyway) enjoy these moments when I'm entirely in One Time, or call it timelessness, and the sense I'm in connection with another species. Clicker training can be extremely effective, but like so many things, it's more effective when you allow it to happen, instead of trying to force it.
I guess my suggestion would be to ask yourself exactly WHAT you want your horse to do, and then try to think in her terms, of what would make this action seem like a good thing. If you THEN give the click, the click will still be associated with something "good."