It helps to cut and slice something strange like that. And measure it or place a familiar object next to it for scale so we know how large it is. You can't really tell for sure what it is unless you examine it thoroughly.
There is a condition call internal laying, and eggs get detoured into the abdominal cavity and they sit there for a while and the hens body heat literally cooks them. Slicing one of those will reveal a hard boiled egg inside.
You can post all sorts of photos, but they are two dimensional, meaning we can't see all around and under and over the object. We can't smell it, either. We rely on your thorough descriptions telling us these things we can't know from a flat internet pic.
Your description of egg yolk from breast to shoe, is it referring to your mom or your hen? If an egg ruptured inside, the egg will be dripping out of the vent and the hen would be straining to get it all out. The hen usually feels sick during the ordeal.
