Looks like what you are looking for is in ow_system_plugins/components/user_list_widget.php

The array defines the order of the list. Down the page you will see that one of the menu items is set to active =>true. That will be the highlighted menu item.

If you make changes, you will need to set dev mode to true in the config.php, and refresh any page on your site after the changes to have them take affect. Set dev mode back to false when you are done.

Note: Make a back up in case something doesn't go right