Fisher and Reynolds were neighbors, living next door to each other in the same Hollywood compound.
The 84-year-old had been rushed to hospital in "fair to serious condition", paramedics told AFP, after collapsing at the Beverly Hills home of her son Todd Fisher.
He said relatives were gathering over the weekend to firm up funeral arrangements, including dates.
The festive season is usually a time of great joy, but at the very end of 2016, our hearts were filled with sadness for the loss of three inspiring showbiz icons - George Michael, Carrie Fisher and her mother Debbie Reynolds.
Debbie Reynolds passed away on December 28th merely one day after her daughter Carrie Fisher died from a heart attack. It is to be broadcast on HBO early next year.
Principal photography on the film concluded in the summer, but plot details, including what part Gen. Organa plays in the story and how the character might evolve or move forward in the already announced "Star Wars: Episode IX", are now unknown. "But now it's a testament of love".
Bloom said, "We didn't know when we would stop or how far back we would archive, but the axis on which the film turned was their relationship and their love - even though showbiz warps the best of people and warps the best of relationships, and I'm sure to some degree they would agree it's warped their family".
And her death came just after Debbie - who had Carrie with her ex-husband Eddie Fisher - posted a heartfelt message to her late daughter on social media.
The documentary, whose producers include Mr Fisher, was mostly shot 11/2 years ago, though it also includes unused offstage footage from Wishful Drinking, a screen adaptation of Carrie Fisher's one- woman show of the same title that aired on HBO in 2010.
"She wanted to be with Carrie", he was quoted as telling industry weekly Variety magazine.
"It wasn't that she was sitting around inconsolable, not at all", her son recounted in excerpts from the interview published by ABC.
Adding: 'I can't imagine what Carrie's daughter, Billie, or her brother, Todd, or anybody who is that close to them is going through.
"In those precise words, and within 15 minutes from that conversation she faded out, and within 30 minutes, she was gone".
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