Great, thank you for this advice!! This is so helpful. I can try and get a pic of the poop, but I think it might have been liquid from a soft shell egg as posted in my update
Edit as of Thursday morning: perhaps I wasn't overreacting. I found these two eggs(?) in the coop this morning (please tell me it's not lash egg). One was in the nesting box and the other was under her roost.
For context, she gets fermented layer Feed, regular layer Feed, oyster shells, grit...