How can I rename the element to in my RSS?

Bearing in mind my comment about, you can use the rss_item hook to add a filter that will let you add the <author>element to your feed

function add_author_to_feed($feed) {
  $feed .= '<author>' . the_author_meta('user_email') . '</author>';
  return $feed
}

add_filter('rss_item', 'add_author_to_feed');

(note – this code is not tested)