Sounds like she wants to nest. I have a female tiel (caged alone and no other male birds) that nests every so often in the corner of her cage on the floor. Sometimes she even lays a few eggs and broods over them for a couple of weeks.
If she's eating, drinking, has clean, bright eyes and clear nasal passages, along with a clean, clear vent, and interacts as normal, then she's most likely fine.
How old is she? My tiel began wanting to nest around the time she was a year to a year and a half old.
First of all, keep an eye on her beak if her nares are a little red; she may be coming down with a cold. Make sure she keeps acting healthy and alert, with no nasal discharge and consistent sneezing or congested breathing. If she starts fluffing up, sleeping alot, and losing her appetite, take her to a vet.
You can put something in the bottom of her cage if you want, but that will encourage her to brood. And when female birds brood, they get a bit territorial. She may lay an egg or more if left how she is, but she probably won't do much with it and you may be able to get it out of the cage easily (if she's not protective) because there's nowhere that she thinks is a good nest for it. If you do let her brood an unfertilized egg in a nesting area, she may sit on it for a couple of weeks and be very territorial and not want to interact much with you.
My tiel will brood an egg on the bottom of her cage for maybe a week, then she ignores it. When I gave her a nest once, she brooded over the eggs for about a month and she was a tempramental little thing!
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