Officers are examining whether the drink contained mushrooms, The Age newspaper reports.
The death of the 53-year-old at a retreat in the town of Clunes is being probed by detectives from the Moorabool Crime Investigation Unit.
A spokesperson for Victoria Police said it's believed the Ringwood North woman became ill after ingesting a drink about 12pm on Saturday.
Two other people were taken to hospital.
The investigation is open and a report will be prepared for the coroner.
The retreat describes itself on social media as an alternative and holistic health service.
A planned event described as "sound healing" was cancelled on Sunday.
On Friday night, the retreat hosted an event with a medium where guests were given a chance to "ask questions of the spirit communicators".
Clunes is about 30km from Ballarat, which has experienced a series of tragic events in 2024.
Since February three local women, Samantha Murphy, Rebecca Young and Hannah McGuire died allegedly at the hands of men.
Miner Kurt Hourigan died in a mine collapse in March and the area experienced bushfires over summer.
AAP has contacted the owner of the retreat for comment.
6°C