She's back to her ornery self, so that means she's fine.
We don't really know what happened and are getting various theories as usual. Peter thought we had run her too hard on the trail after not riding her much last week, and that she didn't get enough water. Dr. Leslie thought it was Lena's cycle causing internal discomfort. Peter didn't agree, but that would make mares different from every other female species on the planet, so who knows.
By the way, we didn't ride her very hard at all - it was only a 2-hour ride with a break in the middle - and it was only in the mid-seventies where we were in any case. We also offered all three horses water afterwards and none of them were interested in doing anything but sloshing it around and onto Katie's shirt.
All in all, there are some days I really wish horses could talk.