Tumor? This one has me really stumped

Cochin hen about 16 months old bottom of pecking order but doing well otherwise. Noticed a pasty butt last weak and ended up giving her a bath today because it was a bit worse than I thought (she enjoyed the bath immensely) After getting her wet I noticed a decent sized (almost baseball size) tumor like mass under the skin starting an inch below the vent and just sort of hanging there. Its weird, I hold her a couple times a week and have never noticed it....but she is a feathery and full bodied cochin after all. Never exhibited any other signs or symptoms of anything. I have racked my brain over this. it should be a little firmer and a bit higher up if it was an egg bound shouldn't it? I've been lucky enough to have never had a hen with one, so maybe im wrong? but what in the world could it be otherwise?

Chris, Dawg, I need your brains here.......

 

could be.....It is not very firm, half way between mushy and firm I'd say? She seems healthy and happy otherwise. I've never seen anything like it though.