The 48-year-old singer's lifeless body was found slumped in the bath of her Beverly Hills hotel suite on February 11, and cousin Dionne thinks her heart simply gave up.
She said: ''You know, in all honesty, I think she had a heart attack, that's what I think happened to her.''
The results of a toxicology report are still pending to determine whether DRUGS played a role in Whitney's demise, although Dionne insists: ''I don't know if it's that or not. I think her heart just gave out.''
The 71-year-old soul singer - who was called to the hotel suite as soon as Whitney's body was found - admits she is still battling to get her head around the loss.
She told American TV show 'Entertainment Tonight': ''When I got there, it was not a pleasant arrival, you know it was just not to be believed and still is not to be believed, I'm still struggling with that, very, very much.
''That this wonderful young lady is no longer with us, physically. But emotionally, her spirit will run around this world for the rest of our lives and all of those who thought of her in that fashion. They'll always remember her, you know, she was a good girl, she really was a good little girl.''
With a new studio album in the pipeline, which includes songs written especially for her by Burt Bacharach, Dionne believes music has been helping her stay strong.
She explained: ''I have not had an opportunity to just let it go. As I said, recording has been a blessing for me. It's taken me out of a reason to just break down. I know it's coming. I know it's going to come soon and I'm looking forward to it. I really am. I want to get it out. I want to have a peace that I know she's enjoying right now.''