According to the book, titled The Mother, Wenche Behring Breivik wanted to mount a soapbox in central Oslo.
"Dear countrymen!" she wrote in the speech she prepared for the day. "The one who caused this tragedy also struck me."
Breivik's mother read a draft of the speech to the book's author Marit Christensen when they spoke on the first anniversary of the killing in July 2012.
According to the book, Wenche Behring Breivik planned to say that she wished her son had died during his twin attacks. Then the only contact she would have had to have with him would have been at his grave.
"Now I have to think about how he's doing. It's worse! His punishment is also my punishment," she wrote. "I has been awful sad and I have cried a lot."
Christensen's publishers Aschehoug on Wednesday announced that they were bringing forward the book's publication by two weeks, catching out Wenche Behring Brievik's lawyers, who were planning to launch legal action to block the book.
Yesterday it emerged that Åsne Seierstad, the Norwegian journalist who wrote the Bookseller of Kabul, also spoke to Breivik's mother, interviewing her in the hospital where she was being treated in the days before she died.
Seierstad's interview has generated a new controversy, as Christensen claims that she broke into the hospital unannounced and forced the dying woman to give an interview.
Seierstad's publisher Erling Kagge on Wednesday condemned the accusations as "completely incorrect" in a letter written to Aschehoug's directors.
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"The meeting was an agreed interview, which lasted an entire afternoon. The interview ended with Wenche Behring Breivik and Seierstad agreed to meet again, something that could not be accomplished because of Wenche Behring Breivik's health," he wrote.
It was important to hear Wenche Behring Breivik's story about her son's childhood, adolescence and especially the time after he moved home," Seierstad said. "I requested an interview through her lawyer Ragnhild Torgersen.
One of Wenche Behring Breivik's last wishes was to stop Christensen's book, after she lost faith in the journalist, and began to suspect her intentions.