Her career spanned 34 years and 57 films-from Miracle on 34th Street to The Quiet Man. But when fiery redhead Maureen O'Hara retired in 1972, she didn't look back. ''I never, ever intended to go back into the movies,'' swears O'Hara, 70. So how did writer-director Chris Columbus (Adventures in Babysitting) get her to costar with John Candy in his upcoming romantic comedy Only the Lonely? He wrote her the perfect part. Candy plays a cop whose mother prevents him from marrying a mortician's daughter (Ally Sheedy). ''I am his Irish, impossible, horrible, awful, nasty, mean, delightful, charming, warm mother,'' says O'Hara.