I agree with the backwards sleeper that is difficult for the child to remove and therefore she cannot access the diaper. I haven't had this situation but I've had TWO situations over the years of "poop explorers" - children who when they have soiled themselves, put their hands down their diaper and then it's on their hands and everything they touch. And they are quiet about it.

Have a video monitor in the room with this child and keep a close eye on the child. Or move the child down to nap wherever you are so that you can watch for the second they wake and nip it in the bud before they get a chance to remove the diaper.