What version of Pages, on what version of OS X? This is important because there are multiple choices whose complete answer will vary based on that question.
Double-click on the Trash icon, locate the Pages document, and right-click on it. There should be a Put Back menu item, that will do as it suggests, placing the document in its original location before it was moved into the Trash. Now, open this Pages document, and visit the File menu, and select the following:
File > Revert To > Browse All Versions…
Just go back in time until document content appears, and then restore that content, providing this is the actual document that your daughter lost. The Finder, not Pages, is responsible for servicing interactive user requests that put documents in the Trash.
It is a good future habit that when your daughter creates a new document, that she immediately save it, even if it is still empty. It is also a lifesaver to have a regular Time Machine backup to an external drive.