She is being questioned on suspicion of withholding information in relation to the savage gun murder of Eamon Kelly in Killester, north Dublin, last December.
She was being held at Clontarf Garda Station last night and is the third woman to be arrested in relation to the high profile murder.
A senior source told the Herald: "Her arrest is part of an information gathering exercise by the investigation team. More arrests are planned including a man that is well known to her. She's not suspected of having taken any active part in the murder."
A total of eight people have been arrested as part of the murder investigation.
Sean Connolly (34), of Bernard Curtis House, Bluebell, Dublin 12, has been charged at the Special Criminal Court with murdering Kelly at Furry Park Road, Killester, on December 4, 2012.
Connolly was also charged with IRA membership on the same date and with possession of a firearm on the same occasion. He is currently on remand in Portlaoise Prison.
Earlier this month, it emerged that Connolly will indicate how he intends to plead to the charge at Special Criminal Court next month.
Eamon Kelly was considered the godfather of Irish crime because he was involved in serious organised criminality for over four decades. He mentored modern-day gang bosses like slain gangster Eamon 'The Don' Dunne, and had a close friendship with former INLA chief Dessie 'Border Fox' O'Hare.
He was the first person of significance ever to be convicted for trafficking cocaine into Ireland. Not surprisingly, Kelly was a long-term IRA target.
The 65-year-old gangster – who spent his days drinking in a local pub and placing bets in a nearby bookies shop – had previously cheated death when the Real IRA tried to murder him in September, 2010.
At Kelly's funeral mass in Killester, Dessie O'Hare said in a rambling church speech: "I would like to emphasise the sacredness of Eamon's life as a reflection of Christ's life.
"Eamon, as you know, had suffered. Jesus, too, was sent by his father to suffer."