Sorry, I should have been more clear. I ran the de-DRM first by importing the book to Calibre with the plugin already correctly configured.
I then used Calibre’s conversion tool to convert to EPUB, just to confirm that de-DRM had actually worked. The conversion tool throws an error if the file still has DRM on it. (The conversion button is on the left side of the toolbar, at least in my installation. Clicking it with a book in Calibre’s library selected brings up a dialog box where you can tweak the settings; options for the output format are at the top right.)
Good luck! You may need nothing more than to have your friend look up the serial number of the Paperwhite and send it to you. 