She had (and still has, as far as I am aware) a brain roughly the size of New Zealand, and was incredibly well-organised and well-informed. She was also disconcertingly and (in my opinion) refreshingly direct and honest. Tact wasn't her strong suit. A summary of a conversation with a fairly inexperienced journalist who shall remain nameless and who I will call DF, went roughly thus:
DF: "You've put in place measures regarding the Monopolies and Mergers Commission."
MB: "Yes, obviously. Is there a question here?"
DF: "Do you think they'll solve the problems the MMC face?"
MB: "If I didn't, I wouldn't have proposed them."
Personally, I enjoyed getting straight answers to questions, but her lack of ability to charm and schmooze the media explains why she never progressed any further than she did.
If she was leader of the Labour Party for the 1997 election, she'd have become Prime Minister. Not with Blair's huge landslide, but the Labour victory in that election was inevitable. Her leadership would have been that of a technocrat, concentrating on getting the decisions right (as best they could), and not worrying about the presentation of the decisions. The media would have hated her, and have been looking for opportunities to target her and the government.
It's unlikely she could have pushed through the Good Friday Agreement.