Alix Tichelman pleaded guilty to involuntary manslaughter and drugs charges, which resulted in the 2013 death of Forrest Timothy Hayes.
Tichelman did not seek help for Hayes when he passed out after she injected him with heroin onboard his yacht.
Police say she was a prostitute and the pair had met on several occasions.
The plea on Tuesday came as part of a deal that included a reduced manslaughter charge.
Tichelman's lawyer, Larry Biggam, said he expects his client to serve only three years. She will will receive credit for the time she has already served - nearly a year.
Mr Biggam said that Tichelman agreed to the plea deal in light of the evidence in the case.
Tichelman was seen in a surveillance video gathering her belongings, stepping over Hayes' body, finishing a glass of wine and lowering a blind before leaving the yacht. His body was discovered the next day.
She was arrested eight months later.
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