The woman left in a critical condition after being assaulted in Co Tipperary has been named locally as Scarlett Faulkner.
Gardaí believe Ms Faulkner, a mother of one from Co Limerick, was attacked by two people on the R494 at Birdhill near the M7 in Tipperary shortly before 5.30pm yesterday.
It is also believed that other people were present when the assault happened.
Ms Faulkner suffered severe head injuries and was airlifted to University Hospital Limerick, before later being transferred to Cork University Hospital.
Her condition has been described as critical.
Gardaí have conducted a technical examination of the scene.
A witness appeal has also been made.
Anyone who was on the R494 between Birdhill and the M7 motorway between 5pm and 6pm yesterday, or anyone with camera footage including dash-cam, has been asked to contact Nenagh Garda Station on 067 50450, the Garda Confidential Line on 1800 666 111 or any garda station.