Thanks - I had a pre-purchase exam when I bought her and the vet did a thorough job of checking her spine. I've read that can be a possibility, so I have been paying attention if pain may be associated with her behavior. Can spine pain just devolop without injury?

You may want to have her Spine checked out with a Vet, Equine Chiropractor, or Equine Massage Therapist.

I bought a quarterhorse mare about 1 1/2 years ago, and to my fault, I haven't spent the time working with her as I should. She seems to have some nasty habits, and one is biting at me when I put the saddle on her (even just setting it on her back sets her off). When I'm on and ask for a trot in the arena, she rears and it's very difficult to get a trot from her. She also turns her head to bite at me. I use squezing of the legs and a clicking sound to encourage the trot, but I can spend a full two minutes on this (in between rearing) before I get a trot. I want her to enjoy a ride, not dislike it, and I feel like she isn't enjoying riding. I've switched saddles and it's the same. She has 5 acres to roam around on, and comes easily when called. She lets me bridle her easily as well. She will also nip out at me across the stall when I'm with my other horse. Any suggestions on how to "get the bite out of my mare"? Thanks!