She'd be fine in canter and walk. I wondered if maybe she was lame (to my knowledge, I've never ridden a lame horse, so I wouldn't be certain) but I lunged her and she didn't seem bothered at all in trot. I'm wondering if her saddle is perhaps pinching her. She's put on a lot of weight recently and I imagine it would be worse with a rider in the saddle but I'm not sure.
Does anyone have any idea what the problem could potentially be, or has experienced similar problems with their horse?
She also coughed a few times when we moved up into trot, if that's any help.
Thanks for reading and I'd really appreciate any ideas.