Erin Patterson was arrested by homicide squad detectives at her home in Leongatha in South Gippsland just after 8am on Thursday.
A search warrant was executed at her Gibson Street home with assistance from Australian Federal Police detector dogs.
Police say she will now be interviewed and the investigation remains ongoing.
Heather Wilkinson, 66, her sister Gail Patterson and brother-in-law Don Patterson, both 70, died after falling ill following a lunch at Ms Patterson's home in Leongatha in July.
Ms Wilkinson's husband Ian, 68, spent close to two months in hospital critically ill.
No charges have been laid.
Homicide detectives previously named the Pattersons' daughter-in-law Erin Patterson as a suspect as she cooked the lunch that is believed to have led to the deaths.
She has previously been interviewed by police and was released without charge.
In a statement to police obtained by the ABC, Ms Patterson said she made a Beef Wellington using button mushrooms from a major supermarket and dried mushrooms bought at an Asian grocery store.
The 49-year-old said she ate a serving and later suffered bad stomach pains and diarrhoea, contrary to the suggestion of detectives that she did not fall ill.
She has previously denied any wrongdoing.
Victoria Police have not commented on Ms Patterson's statement other than to say it was not one taken by officers.
TIMELINE OF SUSPECTED MUSHROOM POISONING
• July 29 - Extended family share a meal at Erin Patterson's home in Leongatha in southeast Victoria
• July 30 - Heather Wilkinson, Ian Wilkinson, Gail Patterson and Don Patterson taken to hospital after becoming ill
• August 4 - Heather Wilkinson and Gail Patterson die
• August 5 - Don Patterson dies
• August 5 - Police execute a search warrant at Erin Patterson's Leongatha home and question her before she is released pending further inquiries
• August 7 - Erin Patterson denies any wrongdoing when questioned by reporters outside her home
• August 14 - ABC releases a letter penned by Erin Patterson in which she says she regrets giving a "no comment" interview to police.
She confirmed she prepared a Beef Wellington for the lunch, claiming she used button mushrooms purchased from a major supermarket and dried mushrooms bought at an Asian grocery store in Melbourne
• August 31 - Public memorial service for Gail and Don Patterson
• September 22 - Ian Wilkinson leaves hospital after almost two months of treatment
• October 4 - Public memorial service for Heather Wilkinson
• November 2 - Erin Patterson arrested and interviewed while authorities search her home with assistance from Australian Federal Police detector dogs
