Gardaí believe a woman discharged the gun that left three people, including a baby, wounded in west Dublin.
A shotgun, which gardaí believe was used in the attack, was found during a search in Dublin on Tuesday. And during another Garda operation a woman was arrested for questioning in Brittas, Co Wicklow.
The 23-year-old female suspect was taken to Dublin and is being questioned on suspicion of involvement in the shooting.
She is being held under Section 30 of the Offences Against the State Act at Blanchardstown Garda station. She can be questioned for up to 72 hours without charge.
The shooting occurred at Parslickstown Gardens, Mulhuddart, on Monday in a development where a number of settled Travellers live.
Gardaí believe the gun was fired into a house from across a nearby street.
A man in his 30s detained on Monday in Mulhuddart shortly after the shooting was still being questioned by gardaí on Tuesday night. He was arrested after ammunition was found in Mulhuddart.
The shotgun and the shotgun cartridges found on Monday were discovered close to the scene of the shooting.
Detectives are working on the theory that a family-based dispute has arisen because of a romantic relationship between a man and woman. And they believe the shooting represents an escalation in that dispute.
Lynn Doyle (29) and her eight-month old son were wounded, along with a 17-year-old relative. All three were sprayed with shotgun pellets.
Other members of the family said Ms Doyle and the wounded teenager were putting up a Christmas tree when the shots were fired.
It is understood the 17-year-old and the baby were at the front of the house when the first shot was discharged from across the road. And when Ms Doyle ran out of the house she too was wounded.
The baby suffered wounds to the leg and body while the male teenager was wounded in the stomach and chest.
