I just looked up what a breast blister looks like and that is definitely what it looks like. I don't believe she's going to make it the rest of the day. She is breathing very shallow now and not moving around at all. Thank you for all your help I really appreciate it. I'm not quite sure how she got it none of my other hens have ever had this problem. Very strange.
Sounds like she's been sick for quite some time, so she probably got it from spending much too much time sitting on a hard surface.