Chicken had difficulty breathing..

Hi guys, I'm extremely new to chickens. I had a free range RIR that started waddling last night. We brought her in since we noticed her chest was swollen, I was afraid of coccidia, but noticed that her vent was clean and her breathing wasn't labored. I researched a bit and figured it was sour crop so I gave her ACV in her water. She was pooping just fine though. It was grassy green with some white. This morning she seemed better but wasn't really drinking water. She would squawk when I'd try to induce vomiting so I stopped. I noticed she had a huge lump, maybe golf ball sized, on her lower abdomen by her right leg. I came back an hour later to try again and she was gasping for air. I tried my hardest to help her but unfortunately I lost her. I'm so confused as to what happened.

I have more chickens, and I'm afraid that it's something serious going on. Any input would be appreciated. I've tried researching but I'm not coming up with anything. This started with a waddling chicken, 24hrs later she was dead.

I'm just bumping your thread hoping you get an answer! Sorry for your loss.