Mrs Balzan-Rudolf, a Swiss national, had been living on Koh Maphrao for around one year.
Her body, dressed in a bathing suit, was found by a fisherman, floating in the sea near Koh Mali on June 16.
She had sustained an injury just above her left eyebrow consistent with having hit her head on rocks.
There were no other injuries to the body, leading police initially to believe that her death was an accident.
On Wednesday, however, Pol Lt Col Sian Kaewthong of Phuket Town Police Station revealed that Mrs Balzan-Rudolf had left a note in which she explained that she had a heart condition and was worried about becoming a burden on her sons, Rolnan and Kelvin.
The autopsy showed that she had drowned, but that her blood contained high levels of sleeping pills and alcohol. Police hypothesise that after swallowing these, she swam out to sea, lost consciousness and drowned. The wound on her head was post-mortem.
Mrs Balzan-Rudolf’s body was cremated on Wednesday evening at Wat Latti-Wanaram (Wat Tai) in Chalong.