Police were called to North Terrace, Adelaide, shortly after 2am on April 25 after a man was found lying in the road, suffering from multiple stab wounds to the chest.
The 25-year-old Victorian man died at the scene.
Police earlier alleged that the killing was the result of escalating violence between two youth gangs.
Two Victorian men, aged 17 and 21, have already been arrested and charged with murder and remain in court.
A 19-year-old South Australian woman was arrested on Friday and charged with assisting an offender.
He was granted bail and will face court in October.
“Enquiries are ongoing and police have not ruled out further arrests in relation to this matter,” South Australian police said in a statement.