I talked to her owner (who is an older, wiser, very reputable trainer in our region) who gave me a little more of the "skivy" on poor Katie. Apparently she was leased last summer to a gentleman who wanted to show her Western Pleasure. Unfortunately Katie's nature was more of a nice canter than a western pleasure lope. So he put all sorts of equipment on her to try to FORCE her into what he wanted. After months of fighting with her he said the horse was incapable of doing it and he gave up on her.
I think what I am getting is the result of this, and I think she is very confused regarding what she is supposed to do when loping. After finding out this info I tried asking her to a canter, giving her plenty of rein and trying to encourage her to stretch out but instead all I got is a humped back, and sort of a crowhoppy, rattlesnake stomp, offbalance falling into the shoulders sort of thing. She doesn't snort, put her ears back or act in any way agitated or nervous while doing this. I am really at a loss as to how to help her to relax and go with what is natural for her.
I was told she was also very good at flexing years ago, and yet she now turns like a giant bus. I have been trying flexing exercises with her and she is fine on the ground, but once on her she is straight as a board with no turn of the head and neck at all. I think this guy really messed up not only her lope/canter but also her balance.
I'm currently riding with a simple D ring snaffle and using a bareback pad..and I really don't think any of the tack is causing pain.