Here's an update for anyone who may still be following this thread. The good news: the fish is still alive! The bad news: the fish still has a prolapse. I followed the treatment outlined above and used a combination of epsom salts and peas. There was minimal change in the prolapse. For a while, it turned very pale and almost white - like your skin after you soak in the tub for too long. Afterward, it turned back to the original pink and lately has gotten a little bit red, which concerns me. I'm keeping the water pristine, which should hopefully help ward off infection.
Does anyone have suggestions on what to do now? The fish doesn't seem lethargic at all. I think it can survive with this, but I'm not sure. I am reluctant to place it back in the main tank because, as Melody pointed out, other fish will probably pick at it. For now, it seems to be doing well in a ten gallon quarantine tank. Any advice would be appreciated. Thanks!