These threads may be helpful to you. https://www.backyardchickens.com/forum/viewtopic.php?id=362422
https://www.backyardchickens.com/forum/viewtopic.php?id=195347
The mass you are feeling could be solidified infection/egg yolk cooked together in her oviduct or abomen. That is internal laying. Could be something else, of course, and I'm not saying for certain that's what it is, but I've been through this internal laying/egg yolk peritonitis thing many, many times already with my original hatchery hens, starting when they were just over two years old, then losing them one by one. Just lost one in the last few days (you'll see the thread "Reba is squat walking" here in the Emergencies section) and on internal examination, found a fibroid mass in the oviduct, tiny ball like masses covering her intestines and oviduct surfaces, some cooked yolk in the oviduct, etc. That was ovarian carcinoma. So many reproductive malfunctions these poor hens experience. They can go on for many months before the hen begins to go downhill, lose massive amounts of weight, become very weak, then die.
One hen had to be put down as she was obviously dying, bone thin, with a hard mass in the abdomen. Turned out, the mass was a huge egg with another egg inside that had dropped into her abomen-freak thing, no way to save her.
Hopefully, that is not the case with your hen--just saying what can be going on in there, for educational purposes.
Below is a pic (graphic, so if you're weak in the face of stuff like this, don't look) of the masses we removed from the oviducts and abdomen of a RIR hen who was laying interally for 8 months before her death:
https://www.backyardchickens.com/forum/viewtopic.php?id=195347
The mass you are feeling could be solidified infection/egg yolk cooked together in her oviduct or abomen. That is internal laying. Could be something else, of course, and I'm not saying for certain that's what it is, but I've been through this internal laying/egg yolk peritonitis thing many, many times already with my original hatchery hens, starting when they were just over two years old, then losing them one by one. Just lost one in the last few days (you'll see the thread "Reba is squat walking" here in the Emergencies section) and on internal examination, found a fibroid mass in the oviduct, tiny ball like masses covering her intestines and oviduct surfaces, some cooked yolk in the oviduct, etc. That was ovarian carcinoma. So many reproductive malfunctions these poor hens experience. They can go on for many months before the hen begins to go downhill, lose massive amounts of weight, become very weak, then die.
One hen had to be put down as she was obviously dying, bone thin, with a hard mass in the abdomen. Turned out, the mass was a huge egg with another egg inside that had dropped into her abomen-freak thing, no way to save her.
Hopefully, that is not the case with your hen--just saying what can be going on in there, for educational purposes.
Below is a pic (graphic, so if you're weak in the face of stuff like this, don't look) of the masses we removed from the oviducts and abdomen of a RIR hen who was laying interally for 8 months before her death:
