Aaliyah Jack, 25, was arrested earlier this week in Mississippi on a Louisiana charge of failure to report a missing child.
On Thursday, the Calcasieu Parish Sheriff’s Office added charges including cruelty to a juvenile and second-degree murder.
She remained in custody in Mississippi after her arrest in the city of Meridian.
It was unclear when she would be extradited.
She did not appear in online booking records, and there was no information available on whether she had an attorney who could comment on her behalf.
A Louisiana judge set bond at $9.1 million, according to the sheriff’s news release.
“Although we have upgraded charges on Jack, our detectives still have a lot of work to do,” Calcasieu Sheriff Gary “Stitch” Guillory said in a news release.
“The investigation will continue while we wait for the autopsy results of the victim.”
Authorities have not stated a suspected cause of death for the four-year-old.
Guillory said at a Tuesday news conference that the baby was covered with insect bites but otherwise appeared in good condition.
Guillory called the boy a “miracle baby”, having been spotted crawling in a ditch beside Interstate 10 after two days alone in sometimes stormy weather.
Authorities recovered the dead child’s body on Monday after getting a report of a body in a lake behind a Louisiana welcome centre.
An investigation led police to search for Jack, who was arrested in Meridian while the search continued for her missing baby.
Workers were preparing to search the water behind the welcome centre on Tuesday morning when a 911 call came in from a truck driver who spotted the baby, Guillory said.
