The veteran star famously battled heroin addiction in the 1980s and she is adamant she recognised the signs of drug abuse when she met the Back to Black hitmaker.
She is also convinced Winehouse was aware Faithfull knew about her issues so kept a distance from the As Tears Go By singer to avoid facing her problems.
Faithfull tells Mojo magazine, "I think she was very, very wary of me. She knew that I knew and she didn't want me to say anything. There's a level of narcissism which is all mixed up with self-hatred. I know it well. It's like a glass wall between you and the world, so that all the love that everybody pours onto you, you don't feel it. But I can't think what I would have done apart from take her and shake her! 'You stupid little c**t! Wake up!'"
Winehouse died in 2011 from alcohol poisoning.