Is that egg larger than normal for her? She may have been having difficulty passing it. I would just confirm that the mass found before is still present, just to make sure that having a hard time passing an egg was not her issue. That in itself can make them feel pretty awful. Just confirm...
I'm very sorry about your hen. :hugs
Hens that are bred for prolific laying, ISA Browns being one of them, are not uncommonly stricken with reproductive problems, especially after the age of 2. Those include reproductive cancers and infections. Treatments are limited and usually not very...