Thank you for all of the suggestions. I had her teeth done and currently have her in a leverage bit. Do you think a short shank or long shank on hackamore would be best to try first?
I sounds like a hackamore would work for this horse. I would just find one online. I believe that I purchased one from Dover saddlery and it had been great. If you are looking for something else that could work I would also consider a hacabit
Also look for more leverage bits and and other pieces that encourage a lower headset.
I don't know much about hackamores, but one suggestion, if you haven't already, is to have his/her teeth checked by a vet. They could have sharp teeth causing them to avoid the bit.