Generally, by the time a bird starts to show signs of illness they are very sick, and have been so for longer than we realize. Birds are 'programmed' as a 'prey' species, and so they hide their illness as long as possible, because in the wild the sick would be the first ones sought by the 'predator as their next meal.Some possibilities as to why your bird may sound like that include:
If your bird has had any other behavioral change, however small, I would make it a priority to take her to the vet ASAP (www.aav.org/vet-lookup) . If she is eating a seed-based diet I would be very concerned about Hypovitaminosis A and all the secondary respiratory infections that go along with it. If she has exposure to other birds, I would worry about infectious agents.
No matter what the cause, if you can rule out 'mimicry', she needs to see a vet before she worsens.
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I am sorry that your quetion was not seen by someone sooner. I am glad that your bird is receiving medical help.