First thing that comes to my mind is a plug. A stubborn sticky plug that dont want to move until its forced. It could be Pleurisy , but Pleurisy doesnt usually only last about an hour. Thats usually a longer term thing. Anytime ive had it , it lasted weeks. I was thinking it almost sounds like a stubborn plug that is stuck and trying to move. I am going by what you say about how she says if she forces a deep breath it will start to go away That really sounds like a plug. Pleurisy does not start to go away with deep breaths. If you have pleural rub ( which i had) you aint taking deep breaths for a while. The rubbing is very painful . Only an xray will tell whats going on when it happens.