Gareeca Conita Gordon, 28, previously admitted killing Miss Netts at the shared accommodation where they lived in Birmingham on April 16 last year.
After the murder, she carried out a series of “detailed, organised actions” to suggest that Miss Netts was alive while taking steps to dispose of her body, prosecutors said.
The Crown Prosecution Service told how Gordon contacted friends and family of Miss Netts through messages, emails and voice calls, pretending to be her and indicating she was moving to London.
Gordon is also said to have purchased a circular saw to dismember the body of Miss Netts and made a number of trips to the Forest of Dean to dispose of the remains.
She was arrested after a member of the public reported suspicions to police about a vehicle driving near Coleford on the evening of May 12.
Two police officers attended and saw Gordon standing close to Stowfield Quarry with two large suitcases, which contained the remains of Miss Netts.
Gordon was later charged with murder and was due to stand trial but pleaded guilty to the charge during a hearing at Bristol Crown Court on April 21.
She will be sentenced at the same court by High Court judge Mrs Justice Cutts on Tuesday morning.
Speaking after Gordon pleaded guilty to murder, Lesley Milner of the Crown Prosecution Service (CPS) said: “Gareeca Gordon committed a truly gruesome crime and tried to cover her tracks.
“Thankfully, the remarkable and detailed police investigation in identifying Phoenix Netts led to the CPS building a compelling case against Gordon, which resulted in her pleading guilty.
“She has now accepted the totality and consequences of her actions.”
In November, a Wolverhampton man accused of assisting an offender over the case had the charge against him dropped.