She's just fine going to lessons and shows, thankfully! She's been in other horse's stalls before without problems. I think it was all about being in an alpha mare's stall, with fresh pee in it that I didn't clean well. And then eating grain in there.
She seemed to have a belly ache after I moved her back, so I gave her a little Banamine. Maybe she was stressed before, too. It was a busy day with a lot of the horses moving out (a trainer leaving, no care issues).
The stall was cleaned well (not stripped) and lots of fresh shavings on top now.
She's fine in her new stall.
It went smoothly. Put the hay in and she walked in and started eating.
I think yesterday just went wrong because there was such fresh evidence of the very territorial alpha mare and it got her worked up. No such issues today.