[Adoby]

Calibre doesn't automatically update metadata in the books in the calibre library. Instead that metadata is only stored in the separate database metadata.db. And backed up in the OPF-file that is stored with the book. The reason for this "lazy" data update is that it would be very slow to update all the books all the time you make some minor change of metadata. Instead all changes to the metadata is only stored inside the database. When you use the GUI the latest metadata is displayed, but that is not necessarily what is stored inside the books.

To ensure that the books are updated with the latest metadata you can save the books to disk or do a epub-to-epub conversion, or use the polish feature. You can also use the modify epub plugin to ensure that the epub is updated with the latest metadata.

If you use the save to disk feature, to prepare a folder with books to send to your sister, then those books will automatically be updated with the latest metadata. The folder could then be zipped and mailed or sent some other way.

You and your sister could for instance use a free cloud service to share books. Then you save the folder with books to a shared folder on your computer and that folder is automatically replicated on your sisters computer. You can have one subfolder each and send books that way. After you have added the books you just delete them from the shared subfolder.

In my signature you find one suggestion of a free cloud service, suitable for both Mac and Windows, but there are many others.