After spending over an hour and a half with my horse chiro/massage person, who also happens to be a very good friend. I learned a LOT about why things have been like they have lately.
The reason I couldn't get that long & low, stretchy trot, walk or otherwise... several vertebrae at the base of Brigit's neck were out and she just *couldn't* do it.
The reason I could get a nice bend to the left but not to the right. Her one hip was dropped and sacrum was all weird. After a massage and an adjustment, she looks like she has an entirely different hind end!
And also, as I suspected, my english saddle doesn't fit. It fits her in terms of tree width and the gullet is nice and high for her big withers. However the gullet itself is too narrow and is putting pressure on either side of her spine. No wonder she's unhappy! Not only that but she thinks the saddle is over-stuffed at the back and is putting way more pressure there than anywhere else.
So Brigit is feelin good again and I'm on the hunt for a new saddle. (Or at least a new to me saddle!) I'm ok with that though because I really am glad it's something fixable and not just a major training roadblock. Until then I'll be riding bareback or sidesaddle which is good too!