The 43-year-old singer was detained by police when she landed in Ireland after a flight from New York and was questioned over claims she was violent onboard, and subsequently taken to a local hospital for assessment.
Her mother Eileen has now revealed O'Riordan is struggling to cope with the stress of separating from her husband of 20 years, former Duran Duran tour manager Don Burton, telling Ireland's Limerick Leader newspaper, "She is going through a marriage separation at the moment. That's hard for anyone".
Eileen had been bracing herself for trouble because her daughter is in a "very vulnerable" place.
She adds, "She (O'Riordan) is suffering from a lack of sleep over the weeks and her brain is racing all the time... She is working very hard. When she was in New York, producing a new album, she kept saying, 'When I go home to my mother in Ireland, I will be fine'."
Recalling seeing her daughter in a jail cell, Eileen says, "Dolores was inside a room, she was lying on the floor, curled up. She had her head covered and her face covered up... She was trying to protect herself. I gave her a hug. I tried to talk to her. She didn't realise I was there at all... She didn't know who I was, she was trying to cover herself from me."
O'Riordan is still in Ireland and is being closely monitored by doctors, who visit her at home every day. Her three children Taylor, 16, Molly, 13, and Dakota, nine, are currently living with Burton in his native Canada.
Eileen adds, "They just know that mommy isn't well at the moment."
O'Riordan was released without charge following her arrest.