Ah, that sounds odd.
Have you checked her crop? If it's impacted, ie full of 'stuff', often long grass or hay, then it will block the passage of both food and water to some extent.
If it is that, I syringe some vegetable oil down their beaks and then hold them with their head at least horizontal, if not down a bit and massage the stuff out. It stinks, but they look heartily glad to be rid of it.
The other thing can be gapeworms - when was she last wormed?