This is a great question, and you may have reason to be concerned.
Is your cham doing this when she is sitting under a basking lamp? If so, it is probably her way of releasing excess heat. How are the temps in her cage in general? It could be too hot for her in there.
If she is doing it at random times for no apparent reason, then there may be a problem. This is also an early symptom of an upper respiratory infection. You may want to watch her for signs of slowed eating, lethargy, etc. If you are pretty sure that she isn't doing it because of the temperature, you may want to run her into the vet and get her started on antibiotics.
Heika