IT TOOK FORMER SUN EDITOR Kelvin MacKenzie all of one week to depose Fleet Street's most powerful [and detested] woman - Bridget Rowe, editor of the Sunday Mirror. MacKenzie, whose appointment as MGN deputy chief executive and group managing editor was announced in mid-January, lost no time in making his presence felt. By 8am Monday, Kelv was bestriding the editorial halls of MGN, barking orders into the expletive-filled air - a scenario not greatly to the liking of la Rowe who promptly demanded an assurance from Mirror group chief executive David Montgomery that she was not subject to Kelv's diktat. It is rumoured that the faintest flicker of a rare smile twitched the ends of Mongomery's lips as he expressed his deep regret that he could not give such an assurance. At which Rowe flounced out and announced to her that she was leaving - the cheers were heard as far afield as Orkney.