It's one of the few zoonotic things you can catch from a sheep. It's also called 'soremouth.' It's a viral infection and usually lambs will catch it and you'll have a whole batch of lambs with it. It can spread from the lambs to the ewe's udders and just isn't generally fun to deal with, but goes away like chicken pox in a few to a half dozen weeks.Hope your sister will be ok. What's orf, not familiar with that?
My sister got it pretty bad on her thumb, but hoping she can manage it okay until it goes away.