Born one of eight brothers and sisters in Cabra West, Dublin, she developed a taste for writing at 14 by becoming a regular contributor to the letters pages of The Evening Herald.
By 16 she had obtained a weekend job with the paper writing local footballers sports profiles.
[2] She studied law for a year at University College in Dublin before leaving to freelance for The Herald.
[2] She and her publisher were prosecuted for offending against the Irish Official Secrets Act in 1995, after she used a police memo to write a story revealing that police had prior knowledge of Ireland's greatest bank robbery.
[8][2] After resigning from her position at the newspaper in 2000, Allen sued The Independent, claiming constructive dismissal due to stress and anxiety.