O'Brien is reported to have died an extraordinary death, with one legend stating that she was sealed into a hollow tree in the avenue of Carnelly Forest.
Other legends state that while leading a hunt of Dromoland gentry in near either Cratloe House or Carnelly House, her riding cloak was blown over her head and it startled the horse, which went wild and flung her into a forked branch of a tree where she choked.

In the Dictionary of Irish Biography, the entry for O'Brien records her death as "conventional", and that "in poor health" in her seventies she made a will.
Signed on 7 June 1686, her will requested that she be buried at the abbey of Ennis, and though there is no marker, it is possible she is buried there alongside her second husband, Conor O'Brien.
Others contend that she is buried at Coad Church in Kilnaboy parish, with two of her daughters.

Folklore and legends claim that Lemenagh Castle is one of the most haunted castle ruins in Ireland, with O'Brien's ghost wandering the halls of the ruin, accompanied by the sounds of an evil laugh and the screams of her supposed victims.

There are three known portraits of O'Brien, one held by the O'Brien family, and two in Dromoland Castle Hotel.
The jewellery worn by O'Brien in one of these portraits, dating from the 1640s, includes a "curious" mermaid-shaped pendant.

A slip jig titled Mall Rua, and associated with Máire Rua O'Brien, was cataloged in 1976 by Breandán Breathnach.
O'Brien is reported to have died an extraordinary death, with one legend stating that she was sealed into a hollow tree in the avenue of Carnelly Forest. Other legends state that while leading a hunt of Dromoland gentry in near either Cratloe House or Carnelly House, her riding cloak was blown over her head and it startled the horse, which went wild and flung her into a forked branch of a tree where she choked. 
In the Dictionary of Irish Biography, the entry for O'Brien records her death as "conventional", and that "in poor health" in her seventies she made a will. Signed on 7 June 1686, her will requested that she be buried at the abbey of Ennis, and though there is no marker, it is possible she is buried there alongside her second husband, Conor O'Brien. Others contend that she is buried at Coad Church in Kilnaboy parish, with two of her daughters. 
Folklore and legends claim that Lemenagh Castle is one of the most haunted castle ruins in Ireland, with O'Brien's ghost wandering the halls of the ruin, accompanied by the sounds of an evil laugh and the screams of her supposed victims.
There are three known portraits of O'Brien, one held by the O'Brien family, and two in Dromoland Castle Hotel. The jewellery worn by O'Brien in one of these portraits, dating from the 1640s, includes a "curious" mermaid-shaped pendant.
A slip jig titled Mall Rua, and associated with Máire Rua O'Brien, was cataloged in 1976 by Breandán Breathnach.
Máire Rua O'Brien