Actually, given that she originally asked for WATER, and was mistakenly given that jug of BLOOD instead, it seems obvious that she was just choking on some errant chunk of half-chewed food.
I'm gonna have Patchouli be my Onee-sama!!β₯Starting today, we'll serve that to Patchouli-sama.WHAT!?SO COOL!!That worked surprisingly well.She gulped it down like a vampire.