That symptom (the posturing) definitely sounds gastro - my Marcel used to do that when he had GI issues as a pup (post-giardia x 4mths) - down on front legs, but in air.
Btw, was the soup low-salt? If no, do you think she was constipated yesterday from the extra salt? Was her poo after the posturing (whenever it arrived, that is
), harder than normal and/or was it mucous-y? If yes, it could be the salt. But like you mentioned, this could also be due to the penicillin, cerenia, and/or weird gastro adjustments can happen just when the body is trying to get back on track after *any* previous GI issue (like she just had).
I hope she feels better soon. It sounds like you're really on top of it - and it's great that you got bloodwork done, just to be sure
.