Then probably too young for reproductive problems to show...
Did you give her a thorough exam? Check her crop (shouldn't be hard or squishy), vent should be clean, keel bone (chest bone) should have some muscle attached, overall weight, eyes/nostrils/beak healthy, parasite free (look at the skin, under the wings, all around her tail). Mites can be small, so look carefully.
The only other thing I can think of is she might have a minor injury... came down too hard off the roost and sprained something. Watch how she walks and see if she is favoring one side.
Excellent idea!! That's my first aid treatment for any digestive trouble. Usually works great if you are in the early stages.
Cats are indoor only. Although Dummo (my nickname for Henry) escapes into the garage occasionally. It could have come from there. Maybe rode in on the dog?

It's a mystery.