I bought a chicken that was a year and a half old about 8 months ago. So she's now 2ish. When I bought her she had a bare white spot under her vent. The lady I bought her from said the other chickens had pecked the feathers away. Over time the spot has grown bigger and become swollen. Today I noticed the spot is very big, swollen, red and purple. There's also a buildup of dried poop above it, but not blocking her vent. The spot is hot to the touch, soft but with a firmness also. I've attached two pictures. I didn't want to push too hard on it. The shell of the last egg she laid two days ago had a thin shell. I've noticed her poop had been dark, watery, sometimes with dark seedy chunks in it. My 6 year old daughter said she has seen her throw up dark liquid, but I haven't seen this myself. She is getting around fine and eating well. She's almost always waiting for us at the back door. She's been like this since we got her. Another detail that may be important is that when I bought her and her sister right away they got a respiratory illness and gave it to the rest of my flock (didn't know at the time about keeping them separate for a bit). I treated them with antibiotics but her sister died. I've read this could be an egg stuck inside of her but I haven't found consistent information. She's one of the favorites. I hope we can help her! Any advice appreciated.