SPRINGFIELD, Mo. » A southwest Missouri woman has admitted to plotting with a daughter to fatally poison her husband and son with antifreeze and attempt to kill another daughter over a 14-month period.

Diane Staudte, 53, of Springfield, pleaded guilty today to one count of first-degree murder, one count of second-degree murder and one count of first-degree assault, The Springfield News-Leader reports. Another daughter, 25-year-old Rachel Staudte, pleaded guilty earlier to helping with the poisonings at her mother’s insistence.

As part of a deal with prosecutors, Diane Staudte will avoid a possible death sentence. She faces a sentence of life imprisonment without the possibility of parole.

Staudte told investigators that she poisoned her 61-year-old husband, Mark Staudte, with antifreeze because she hated him, and that she killed her 26-year-old son, Shawn Staudte, because he was “worse than a pest,” according to the probable cause statement. She also admitted poisoning her daughter Sarah Staudte over four days because “she would not get a job and had student loans that had to be paid,” investigators said.

A medical examiner initially ruled that her husband’s April 2012 death was from natural causes and her son’s September 2012 death was from prior medical issues. But a tip led authorities to re-examine the deaths in June 2013 following the hospitalization of Sarah Staudte, who was then 24.

Greene County Prosecuting Attorney Dan Patterson told the judge that Sarah Staudte suffered physical and brain injuries after being poisoned. He said the college graduate has a guardian and lives in an assisted living facility.

In a statement that Sarah Staudte read in court, she said she forgave her mother.

“Not only she took away my dad and brother, she also took away my livelihood and my independence,” the statement said. “I prefer to be a survivor than a victim.”

Diane Staudte admitted under questioning that she poisoned her family by putting antifreeze in their soda and Gatorade. She originally told police she was the only one involved. But after Rachel Staudte admitted to taking part in the poisonings, Diane Staudte told investigators that the pair had planned, researched and committed the crimes together.

Rachel Staudte’s plea deal said she did not want to poison Shaun and Sarah, but she did so because of her mother’s instructions.

A poem that was found in Rachel Staudte’s purse when she was arrested was read during the sentencing. It ended with the line: “Only the quiet ones will be left, my mother, my little sister and me.”