Tiffany Hall, 24, looked sullen as she appeared at an arraignment hearing via video conference from the St. Clair County Jail, where she is being held on a $5 million bond.
Prosecutors say she killed Jimella Tunstall, 23, who was about seven months pregnant, and her fetus.
St. Clair County Associate Judge Heinz Rudolph entered not guilty pleas on Hall's behalf on charges of first-degree murder and intentional homicide of an unborn child. Each charge carries a penalty of 20 to 60 years or life in prison, prosecutors said. The murder count could be punishable by the death penalty.
According to authorities, Hall told police she also drowned Tunstall's three children — ages 7, 2 and 1 — and stuffed them into a washer and dryer at the apartment they shared with their mother. Hall has not been charged in the children's deaths.
Police have not offered a motive.
Rudolph asked Hall whether she planned to hire a lawyer or needed a public defender. She replied simply: "I don't know."
Rudolph appointed public defender Randy Kelley and granted Kelley's requests for a psychological evaluation and that Hall be segregated from the rest of the inmates for her protection.
"Any time you've got a charge of this nature that has some volatility, I just think it's in her best interest that she be protected from the influence of other inmates or possible harm to her," Kelley said after the hearing.
Preliminary autopsies on the children appeared to show they were drowned, said Ace Hart, a deputy St. Clair County coroner. There were no signs of physical abuse or trauma on the three children and toxicology tests were pending "to see if they were poisoned or possibly drugged," Hart said.
The community turned to prayer Sunday to understand the slayings at a service for the family.
"This is an opportunity for people to turn to God," said Debra Kenton, a member of the New Life Community Church. "Who else can explain things like this?"
In the days after authorities say she killed Tunstall and her fetus, Hall went about everyday life, chatting with her daughter's elementary school teacher and helping her daughter with homework, Hall's mother, Beverly Cruise, told the St. Louis Post-Dispatch for Monday's editions.
An autopsy showed that Tunstall bled to death after sustaining an abdominal wound caused by a sharp object, believed to be scissors, Hart has said. Authorities believe her womb was cut open after she was knocked unconscious.
Authorities suspect Tunstall was slain on or about Sept. 15.