SPRINGFIELD, Mo. (AP) — A Missouri woman has pleaded guilty to her role in the fatal poisonings of her father and brother and an attempt to kill a sister with antifreeze.

As part of her plea Tuesday, 24-year-old Rachel Staudte, of Springfield, agreed to testify against her mother, who is also charged in the deadly plot.

The Springfield News-Leader reports that Staudte pleaded guilty to two counts of second-degree murder, one count of armed criminal action and one count of first-degree assault. She agreed to serve two life sentences and testify against her mother, Diane.

Staudte’s father, Mark, and her brother, Shawn, died in 2012, and her sister, Sarah, became ill but survived. An anonymous tip led authorities to investigate the deaths.

Staudte’s mother, Diane, is scheduled for trial in November.