A Victorian woman has been placed on the sex offender's register for life after being jailed for sexually abusing four girls.

County Court judge Michael Patrick Bourke said 22-year-old Alicia Storrie's crimes against her victims, aged 12 to 15, were exploitative and damaging.

"This was ... prolonged predatory and grooming behaviour against young and vulnerable girls," he said.

Storrie, of Portland, pleaded guilty to 10 counts of sexual penetration of a child under 16 and five of performing an indecent act with a child under 16.

The court heard she assaulted the girls between 2004 and 2008 at various locations in the Portland and Warrnambool area in south-west Victoria.