Ann Heywood told The Wall Street Journal newspaper that that the killing of her son Neil had left his two children, aged eight and 12, without financial security.
She expressed her "disappointment" with Chinese officials for not engaging with the family over the murder in Chongqing in November 2011.
China's foreign ministry did not immediately respond to a request for comment by AFP.
Heywood has been described as close to the Bo family, but the politician's wife Gu Kailai was convicted of his murder last year, when a court heard that they had fallen out after a business deal went sour.
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French court filings obtained by AFP show that at one time Heywood managed a villa in Cannes which was reportedly a fruit of Bo's alleged corruption.
In her statement to the Wall Street Journal, Ann Heywood said that "circumstances now compel me to break my silence".
She said her grandchildren were "particularly vulnerable to the hurt and horror of their father's murder and, since Neil was the family's sole breadwinner, to uncertainty and insecurity, there being no financial provision for their future".
"I hope and trust that the leaders of this great nation, which Neil loved and respected, will now show decisiveness and compassion, so as to mitigate the consequences of a terrible crime and to enable my family finally to achieve some kind of closure to our ongoing nightmare," she said.
The scandal emerged last year ahead of a once-a-decade leadership transition, in which Bo had been considered a candidate for the Politburo Standing Committee -- China's most powerful body.
His downfall was triggered after his police chief and right-hand man Wang Lijun fled to a US consulate in Chengdu city near Chongqing, allegedly to seek asylum. Bo was detained a month later.