My best guess (and that is all it is-with 4 boys I have no "female" keet behavior experience), would be she is trying to nest. As was mentioned, if she is in breeding mode (is her cere dry and crusty?) but NOT with egg, it would actually be good to discourage the nesting behavior with the rocks in the food dish.

That will also create more of a foraging environment for getting the seeds and would be good too.

I have no idea how you tell if she is "with egg" but maybe if you posted that question in the breeding forum? Have you seen any "activity"?