Thanks for that!
She does have a little bit of trouble striking the canter on the lunge right now. I've been told by a previous owner ( a couple of owners ago) that she never used to. She doesn't neccessarily gait on the line though (occasionally she has), generally she will try and "run" the trot into the canter (which I will then slow her down and try again).
As far as we know she's never had any "formal" training to gait. This is something she's doing, to the best of my knowledge, because she feels it's more natural for her. She is very laterally inclined - something many of the coaches her leasor has worked under have mentioned.
She is trimmed to fit her conformation... not to suit a particular "style". I have no idea if this has been the case her whole life, but for the past 3-5 years I know this to be true. (I use the same trimmer as the lady we got her from did)
Her saddle fit has been assessed by a professional and has been deemed "as good as it gets without spending big $$ on a custom saddle". Right now her biggest issue is a lack of topline, making any saddle fit difficult.
I'm not a fan of Chiros in people... originally I thought that was my only option for the horse (in my area anyhow), but it sounds like we have come across a massage therapist/ myofascial/naturopathy practitioner who has agreed to come and assess and adjust her if needed. *yay* I'd just feel better if someone took a look.
Conformationally she's "correct" as far as the breed is concerned. She comes from top bloodlines, has been used as a broodmare and has produced some very high quality foals. That said... she does have the typical hindquarter for the breed, and though isn't as long in the back as some, she's far from having a "short" back too.
Her rider does contribute to the issue, sometimes. Like all riders she's not always totally correct - but nor is she really creating the problem most of the time either. I do find that as she gets frustrated the horse gaits more... so part of it may be a tension issue as well.
We'll have her assessed, then just keep working on gently asking for what we want. If she's determined to gait, I'll have a TERRIFIC trail horse (because she is the most comfortable thing going, and has a really solid mind!) and beginner friendly walk/trot mount and I'm really OK with that (was why I actually wanted her... her recent excursions into the hunter/dressage arenas have been because the leasor wanted to try).