Jessica Ellen Stasinowsky, 20, and her girlfriend Valerie Paige Parashumti, 19, pleaded guilty in December to the wilful murder of Stacey Mitchell.
They admitted in the West Australian Supreme Court to killing Ms Mitchell between December 17 and 21, 2006, while the girl was staying with them at a house at Lathlain in Perth.
Her body was later found in a wheelie bin in the back shed of the house.
During sentencing submissions today, prosecutor David Dempster described how Parashumti bludgeoned Stacey with a concrete block while Stasinowsky strangled her with a dog chain.
The two girls grinned and grimaced at each other as Mr Dempster told the court it took their victim half an hour to die.
Their expressions drew a rebuke from Justice Peter Blaxell.
Under West Australian law, wilful murder carries a mandatory life sentence of at least 15 years in jail, although the sentencing judge can set a higher minimum time.
The court was told the lovers videoed themselves mocking Stacey's semi-naked body, over which they kissed.
They later forced a 15-year-old boy to watch the mobile phone footage and made him help clear up the blood.
Parashumti's lawyer, David Edwardson, QC, said his client was part of a vampire sub-culture and had been interested in drinking blood since she was 10.
However he told the court Parashumti insisted this had nothing to do with the killing.
Instead he said his client appeared to be partly motivated by a desire to dispel any notion she may have been sexually interested in Stacey.
"Both women appeared to be obsessed with proving their commitment to each other,'' Mr Edwardson said.''