Why Is Harriet Harman A Minister?

No, Brown can't sack this ridiculous Castrolater (and man-hating fanatic, erstwhile and unrepentant Hard Left stalwart, old legal stand-by for the Paedophile Information Exchange, &c, &c, &c) as Deputy Leader of the Labour Party. But he is under no obligation to make the Deputy Leader a Minister. And as a Minister, Harman doesn't seem to do anything, anyway. So he should sack her. What is he waiting for?