Deb is always Deb, except occasionally Debra for legal purposes (and her old university boss liked to call her that, because he said that she deserved a more formal name as Executive Assistant to the President). Her family still calls her Debbie (or Aunt Debbie), and somehow when I refer to her to a family member she always get mentioned as Debbie.
I'm the only one who calls her Debster. (Okay, me and some of our Medium peeps.)