The Point Cook townhouse was destroyed in the Wednesday morning blaze, with the bodies of 19-year-old Abbey Forrest, 28-year-old Inda Sohal and newborn baby Ivy found in the ashes.

The intensity of the fire raised suspicions among arson and explosives squad detectives that it may have been deliberately lit, with police arresting Jenny Hayes, 46, in Airport West on Thursday morning.

She was later charged with three counts of murder plus arson causing death, and declined to appear in Melbourne Magistrates Court on Thursday night as her case was briefly mentioned.

Magistrate Luisa Bazzani questioned what the relationship was between Hayes and the family, but her lawyer Erin Byrt said it was yet to be disclosed.

Hayes is due back in court in March.

Abbey's sister Emily visited what remains of the house on Thursday, laying flowers and a Peppa Pig doll outside in a tribute to the "beautiful souls".

"This should be the perfect time of their life," she told reporters.

"Now this awful tragedy has happened."

The young family had only moved to the two-storey home on Totem Way after the birth of their daughter on November 13, Ms Forrest said.

Neighbours have recalled hearing screams and cries for help, with one man said to have thrown an axe and rocks to break an upstairs window that wouldn't open.

Ms Forrest thanked those who risked their lives to try and save them.

A GoFundMe page she set up to cover funeral and memorial costs has raised more than $10,000 in less than 24 hours.

Australian Associated Press