Although Dionne was nervous about addressing her feelings, it gradually became "easier and easier" to speak out.
She told heat magazine: "I think sometimes when you have to take a look in the mirror, it's one of the hardest things to do. "But then, to move forward, I knew I had to put a pin in that chapter. "And the more I talked, the more weight lifted off my shoulders.
"It became easier and easier – talking about her was the easiest thing, which was crazy, because 10 years ago talking about her was the hardest thing."
Dionne hopes the documentary will show how "caring and loving" Amy was. Asked the impression she wants to leave with the film, she said: "Just how caring and loving she was. I think people always think of her as being very out-there and speaking her mind, but she was also so respectful and sweet, and so normal.
"There was no pretension, she was authentically herself. And she had banter for days, that woman.
"If she hadn't been a singer, she could easily have been a stand-up comedian.
"I just want people to see the true Amy I know, because anyone who knew her was lucky to know her."
