Could my horse have a sore neck?

I would have her mouth worked checked on. She could have had problem with her teeth. It would also be her back. Mostly a neck is only sore when you are working in tight circles. She shouldn't be doing that if her neck is sore. Run your thumb down her back on one side (apply pressure) start at her wither and run your thumb down to her hip. Make sure your pressing pretty hard, if she flinches then her back is sore. I would start with that. Hope it helps.