Hi there and welcome to BYC!
Sorry your girl is having trouble.
You gave a good description so far, but I'm gonna ask some more things.. Can you feel any heat or swelling coming from the area, is there any pain response when you feel around or press on it? What is her normal feed routine including treats and supplements? Has she started laying yet and if so when was her last egg? How is her appetite? Is she passing droppings? Where did she come from, how long have you had her, do you know if she was vaccinated against
Marek's or ever face severe coccidiosis as a chick? Ever check or treat for internal parasite load? How about external parasites.. how does her skin look below her vent and on her abdomen.. light flesh colored or angry red? How many birds, in how much space?
Do you have resources to see a vet.. the funds and the vet themselves in your area? It's $65 for an
avian vet visit here. Not including tests or treatments suggested.
I would NOT administer aspirin without confirmation of actual pain.. it is okay for short term use ONCE deemed helpful. Pain is NOT thye evil we think but rather a good thing when it limits our movement and keeps us from injuring ourselves further! It lets us know there is a problem but we still need to identify the source before trying to mask it, in MY experience.
Rest is a good thing but the body is clearly making that happen. I would probably keep her in sight of the flock if possible to reduce stress on her and make reintegration easier IF it is to happen.
Are you able to post any photos of her? How high is your perch, and what is the landing surface under neath? What breed is this gal we're speaking of? Adding your general location to your profile might help folks know what resources you have at a glance since we are gathered here from many countries.
Hope she recovers quickly and you get some answers!