She appears in "The One Where Ross Is Fine" when she and Bill kindly invite Monica Geller and Chandler Bing to their apartment to talk about adopting a child. Chandler goes off to the bathroom, but bumps into Owen and accidentally reveals to the boy that he's adopted which freaks him out and cried "I'm adopted?!" because he never knew. Monica and Chandler try to escape when Chandler reveals to Monica what he did, but they're too late. Owen appears in the living room and once again cries "I'm adopted?!" and tells what happened. This leads to Bill and Colleen hating Monica and Chandler and vice-versa.
Colleen is never seen or mentioned throughout Season 10 again.