Born in Erdington before moving to Small Heath where she spent most of her childhood, Brennan attended Holy Family Primary School.
By 2003 the school was rated as "very good" by Ofsted and had "rapidly and impressively improved over the last two and a half years from weakness to its present high position.
"The Headteacher is relentless in her pursuit for excellence and has brought about significant improvements in the quality of teaching and learning, and the achievement and behaviour of pupils.
Her Majesty's Chief Inspector for Ofsted at the time, Sir Michael Wilshaw, praised Brennan in a letter from 2015 regarding Etone College.
"Your determined and highly effective leadership, and strong support from senior leaders and the governing body, have played a key part in bringing about rapid changes with the college.
The group subscribed to six core beliefs in the report, including how "school leaders have a critical role in establishing high standards of learning, teaching and behaviour.
She was awarded Dame Commander of the Order of the British Empire (DBE) in Her Majesty the Queen's Birthday Honours List 2005, for her services to education.
Brennan was identified in the Dudley report for leading a team of senior managers who EWS (Educational Welfare Service) investigators claim manipulated registers to make the school appear more successful than it actually was.
In their interim report, EWS officers alleged that the records created a false impression of improved attendance which promoted the school's image and resulted in higher pupil numbers.
Teaching Agency presenting officer, Bradley Albuery, claimed evidence of “deliberate” misrecording to “pretend attendance was better than it was” and to boost perceptions of Hillcrest School.
The report stated there was "no suggestion of any harm to children", no "personal financial gain" and Dame Maureen "expressed remorse" and had "an impeccable previous history.