I was thinking abdominal egg laying (and still can't rule it out quite yet) but usually tumors aren't free-floating in the abdomen. Were all of them attached? Or some were, some weren't? IS it possible that the ones in the liver were different from the ones free floating?
I suspect abdominal laying for the free floating ones - they cook in the body and aren't yellow like you'd expect to see yolks be normally quite. But the ones that were in the organs, if they were part of the organ (tumor) then I'd say either Marek's or Leukosis.
Mareks and Leukosis are the 'cancers' of chicken.
They're both viral, both contagious, however Marek's is less so than Leukosis.
Were either of this hens' eyes (pupils to be specific) blind or too large or too small?
If you lose another chicken, especially if it has fluid in the abdomen, or loses weight despite a healthy appetite and correct food, I would take it and have a necropsy/histo done and find out which it was exactly. It may be too late for this girl if you've buried her or haven't refrigerated her. Or you could photograph it and have a consultation done online (highly recommended - PM me if this is the option) which might be more affordable.
I would contact your state's ag colleges and their extensions now, whichever is nearest, and ask that in the case of a necropsy being needed do they need a live dying bird, or a carcass - and if a carcass what do they need you to do? Better to have the information ahead of time than when you're sad or stressed.
I'm very sorry that you lost her, but I think you just caused her some relief and gave her mercy. That's a much better end than suffering. /hugs for your own heart's suffering and that of your baby boy.