Mrs Balzan-Rudolf, a Swiss national, had been living on Koh Maphrao for around one year.
Her body was found floating in the sea near Koh Mali – a tiny island southeast of Koh Maphrao and about 4 km east of Phuket – by a fisherman just before midday.
She was found wearing only a one-piece bathing suit.
She had sustained an injury just above her left eyebrow consistent with having hit her head on rocks.
No other injuries were immediately apparent, leading police to believe her death was an accident.
Kusoldharm volunteers estimated that the body had been in the water for 10-15 hours before it was discovered.
Autopsy results are expected to become available tomorrow.