Speaking exclusively to ITV News, Dawn Bestwick said jail wasn't good enough for MIck Philpott and that "as a coward" he "deserved to die".
The judge has delayed her sentencing to "reflect further" on the trial Mick and Mairead Philpott and friend Paul Mosley.
Tributes have been paid to five brothers and their sister who died in a fire at their family home in Derby in May last year.
The shadow chancellor Ed Balls has condemned the "nasty and divisive" comments by George Osborne in which he questions why taxpayers' money was being used to "subsidise lifestyles" like Mick Philpott:
I believe George Osborne's calculated decision to use the shocking and vile crimes of Mick Philpott to advance a political argument is the cynical act of a desperate Chancellor.
Our main thought at this time should be about the six children who tragically lost their lives, and the others in the family who have been left to mourn their loss.
We should have a proper debate about welfare reform.
And we should discuss what action needs to be taken to tackle the scourge of long-term unemployment including the need for a compulsory jobs guarantee so that people cannot languish on the dole for years and years on end.
But for the Chancellor to link this wider debate to this shocking crime is nasty and divisive and demeans his office.
The sister of Mick Philpott described how she effectively buried her brother today as she saw him sentenced to life for killing six of his children in a house fire in Derby. Speaking exclusively to ITV News, Dawn Bestwick said jail wasn't good enough, and that "as a coward" he "deserved to die".
Dawn Bestwick said: "They [the children] had a life. He [Mick Philpott] took that from them, he had no right. I hate him, I hate him so much. He's hurt us so much, it's not fair. He doesn't deserve to breath God's air. He deserves to die for what he did - and so do the other two. They were so cruel.
"It's not human, he should die for what he did. All three should rot in hell for what they did. The pain we have to live now, the grandmothers, the grandfather - they're the ones suffering too. The other siblings, Lord knows how they're going to get through this. But we're a strong family."
Watch the interview in full here shortly.
– Stephen Timms, Labour Work and Pensions Minister
It is wrong to link those acts with the debate about welfare and George Osborne should not be doing so, even implicitly.
Millions of people including pensioners and the disabled, people in work and out of work, receive benefits and tax credits. The Government needs to recognise that they are as shocked and disgusted by the callous killing of these children as anyone else in Britain.
Where the ultimate blame should lay for the deaths of six of Mick Philpott's children is at the centre of fierce debate.
Editor and founder of the Guido Fawkes blog Paul Staines and Independent columnist Owen Jones amplified that debate on ITV's This Morning.
Paul Staines levelled the blame at the welfare state while Owen Jones said that was like blaming Harold Shipman on the NHS.
Mairead Philpott wept in court as she was sentenced to 17 years behind bars for the manslaughter of six children in a house fire.
Labour MP for Middlesbrough Andy McDonald has accused George Osborne on Twitter of "trying to make capital" out of the Philpott case:
Total disgrace that Osborne tries to make capital out of the appalling Philpott case. Typical Tory demonization of anyone on benefits.
Chancellor George Osborne has said that the case of the Derby house fire raises questions about whether the Government and taxpayers should be "subsidising lifestyles like that".
Chancellor George Osborne has questioned why the taxpayer should pay for benefit "lifestyles" such as those of child killer Mick Philpott.
When asked on a visit to Derby if the Philpotts were a product of Britain's benefit system, Mr Osborne said: "It's right we ask questions as a Government, a society and as taxpayers, why we are subsidising lifestyles like these. It does need to be handled."
He said Philpott "was responsible for horrendous crimes, crimes which have shocked the nation".