That is the most outrageous claim I've ever heard.
Writing the book didn't make her unavailable for employment, she was a single mum! She would have paid tax on the money she earned from publishing the book so I'm pretty sure she paid much more back in tax than she received in benefits.
Some people are just bitter.
As for the way Labour are choosing to spend the money, I think it could make sense because investment into other things could generate more money to pay off more of the debt...
...but investment doesn't seem like that brilliant of a thing right now so I wouldn't get my hopes up on that
I can't imagine wanting to give that kind of money to a political party. Bob Geldof and Bono are trying to save africa, amongst many other celebrities, and good old J K Rowling wants to save Labour. You couldn't make it up could you really.