Please help, I think I accidentally taught my horse to rear?!?

If what you were doing seemed to be working before you had to put her in the pasture, then keep doing that. If you find something that seems to work, you need to keep it up so that she learns that that's unacceptable behavior. It sounds to me like she just needs an attitude adjustment lol. I've found that raising your voice and jerking the halter are usually the best things to do in those types of situations and then when they come back down, turning in the tight circles and backing up lets them know that they were wrong and helps get them back in line and listening to you. Hope this helps!