I talked with the masseuse today. She said that Izzy's back is absolutely fine, but her poor lil' bum was sore, most likely from all the rearing she did on Tuesday.
I'm about halfway through Joyce Harman's "Horse's Pain-Free Back and Saddle-Fit Book" that I got at the library last night. It's an excellent book that I highly recommend buying even if you're not having troubles with saddle fit. As a result of my reading, I decided that Izzy's saddle might be sliding forward which jams it into her shoulders. This morning, following advice from the book, I attached the girth to the front two billets instead of the first and third. I also scooted the saddle back when we switched directions lunging. The sweat marks were much more regular when our workout was done.
All that would mean something if her back was sore at all. If it was hurting her, if there was a physical problem, it would show. It doesn't. She's completely relaxed. The masseuse didn't even charge me because there was nothing to really work on. Izzy loves to have her back curried, hard. I even lunged her for about half an hour today, then rode just a tiny bit at the walk, then had the masseuse look at her and still nothing. Izzy was thrilled with all the attention, though. I'll ask Cathy about ulcers and other possible internal causes, but this mare lives out in a pasture with a friend 24/7. She doesn't get worked up about much. Everything I've done with her has been slow and easy, because she's not a terribly quick learner.
So. Now what? She hasn't given me any trouble mounting since Tuesday, but I've only been on her twice, both times after a very long period on the lunge. I don't want to cause her pain, but she's not in pain. The masseuse did mention that she might be cold-backed, and gave me something to do before I saddle her that should help. I dunno. It's starting to look almost like Izzy's tried to revert back to her days with her previous owner, where she learned some cool tricks about scaring people. She's a smart girl, and she learned that when she was naughty, she didn't have to work. She'd never done that for me, but it could be that I was starting to push her a little and she wanted to scare me in to backing off.
Is that so unreasonable? I guess I'll try for a more normal ride tomorrow. Cross your fingers.