I would take her to the GP. Croup has been going around and is much worse at night. You wouldn't even think they are sick during the day. One time when my son had croup it didn't have the really barking distinct sound to it either so I left it for over a week. It just hung around.
If it is something else then a vapouriser and chest rub should help a bit with her sleeping.

Hope you sort it out soon, listening to your little ones coughing is awful!