A woman has been arrested following the suspicious death of an 84-year-old woman in Sydney's north-west last month.

Strike Force Vado was formed to investigate the death of an elderly woman after her body was found in her home on Comet Street in Melonba near Marsden Park about 12.30pm on October 4. 

Officers established a crime scene and commenced an investigation.

About 3pm today, a 50-year-old woman was arrested on Comet Street.

She was taken to Mount Druitt Police Station, where inquiries were ongoing.

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