Between 2003 and 2007, Koster played for Hunter Jaegers and AIS Canberra Darters in the Commonwealth Bank Trophy league.

[4] Between 2003 and 2007, Koster made 50 appearances for Hunter Jaegers and AIS Canberra Darters in the Commonwealth Bank Trophy league.

In 2007 she played in every quarter for Hunter Jaegers and was a member of the team's leadership group.

She was subsequently named the Netball NSW Marilyn Melhuish Commonwealth Bank Trophy Player of the Year.

She was a member of the Australia team that won a bronze medal at the 2005 World Youth Netball Championships.