Keen-Warren was sentenced to 12 years in prison in 2023.
Her release was not unexpected - Florida law offered her credit towards an early release for good behaviour.
"Sheila Keen-Warren will always be an admitted convicted murderer and will wear that stain for every day for the rest of her life," Palm Beach County State Attorney Dave Aronberg said in a statement Saturday to the Associated Press.
Keen-Warren took the plea deal because she would be released quickly and might otherwise have faced a life sentence if the case went to trial, Greg Rosenfeld, Kenn-Warren's lawyer, told the Associated Press.
"We are absolutely thrilled that Ms. Keen-Warren has been released from prison and is returning to her family," Mr Rosenfeld told the news outlet. "As we've stated from the beginning, she did not commit this crime."
The son of the victim, Joseph Ahrens, told authorities the doorbell rang at their family home and his mother answered the door to a person dressed as a clown. The person handed her some balloons and then shot her in the face.
Authorities said that Keen-Warren was having an affair with the victim's husband but it wasn't until DNA testing improved that investigators connected Keen-Warren to the crime.
In 2002, Keen-Warren married Michael Warren.