Hi Lindak
I've been off the air pretty much and just catching up now.
Well, not to be too personal, but when I've had racing diarrhoea I get a sore red butt too, so not to be too concerned maybe.
Jen's idea of some cream is good. Even paw paw ointment if you can get it there, we have one here called Lucas' Paw Paw ointment which is great for sore skin/itches etc anywhere. As it's plant based if puss grooms and licks it off she's less likely to be affected.
And yes to find out the cause, maybe she just ate something outside that didn't agree too well. Not been chewing any plants or anything? Been near any other cats?
Also hopefully not dehydrated. Definitely worth a vet check even if puss seems better, even if just to help with rehydration/electrolyte balance.
Wishing her well (and you)