Clinging and smothering behaviours are the unsavoury consequences of a deep-set existential, almost mortal fear of abandonment and separation. For the codependent to maintain a long-term, healthy relationship, she must first confront her anxieties head on. This can be done via psychotherapy: the therapeutic alliance is a contract between patient and therapist which provides for a safe environment, where abandonment is not an option and, thus, where the client can resume personal growth and form a modicum of self-autonomy. In extremis, a psychiatrist may wish to prescribe anti-anxiety medication.
Self-help is also an option, though; meditation, yoga, and the elimination of any and all addictions, such as workaholism, or binge eating. Feelings of emptiness and loneliness -- at the core of abandonment anxiety and other dysfunctional attachment styles -- can be countered with meaningful activities (mainly altruistic and charitable) and true, stable friends, who provide a safe haven and are unlikely to abandon her and, therefore, constitute a holding, supportive, and nourishing environment.
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 3 DVDs with 16 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/the...)