Rivers, 47, waited three weeks after her mothers' September 2014 death to explore options for the book's release.
"When I found out (how much I'd get paid)... My mother would have killed me if I didn't do it. It's the one thing I did right," she said.
Curating the collection of stories, letters, and other mementos in "The Book of Joan: Tales of Mirth, Mischief, and Manipulation" gave "me permission to laugh," Rivers said.
Following her mother's death, Rivers was inundated with condolences from Hollywood, including one from Courtney Love.
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"She put out a post along the lines of 'I haven't finished
looking like a mess yet, you can't be gone.' Katy Perry's was 'what's the point of wearing these stupid outfits if Joan isn't around to criticise them?'
"... Those are the ones I loved because it meant they got it - they loved her and saw the humour. They understood it wasn't personal and was funny, and the fact that we could talk and joke about you meant you were relevant," Melissa said.