Ann Pettifor's background appears to be in church groups campaigning for debt cancellation. Her take on debt, in particular third world debt, is primarily a moral one. This is right, as the question only has importance as it is a moral issue. She is also being proven right that, despite what the mainstream news will tell you, the debt crises are gradaully coming closer to the "first world" nations, and will inevitably occur there just as they have done everywhere else.
That said, her understanding of economics and history is a little shaky. In some cases this is only a minor problem, like saying Thatcher was PM in 1978, or the UK lost the Boer War. However, her account of Keynes is a bit mangled, and although she pitches for a moral Guardian-reader audience, her economic understanding probably owes more to writers like Michael Rowbotham. Moreover, although she is justifiably outraged at the dehumanising effects of massive debts, her strident moral tone sometimes reads as if she believes that the banks are run by sadists suicidally bent on causing mayhem for the sheer hell of it. Her attempts at a historical analysis of the development of the modern economy doesn't take into account the fact that economic pressures force people, even those in high places, to act the way they do or else to face bankruptcy themselves.
That said, this is a very timely book, and I'm not sure what other book on this topic is available just now.