Well, there has been a development. She ate the egg! I'm thinking this will replace any nutrients she may have lost. We have replaced it with a fake one for now - my father has bred birds in the past and apparently this is good practice.
She was her usual quirky self last night although a little moody with me, not surprisingly if she is nesting.
When I left this morning she was on the bottom of the cage again so I think she'll most likely lay again today.
Thanks for the replies guys!