Genene Anne Jones, now 63, was convicted of killing Chelsea McClellan, 15 months, in 1982 at a pediatric clinic in Kerrville, Texas.
Jones began injecting the child with a lethal dose of muscle relaxant while the baby was still in her mother's arms, court records indicate.
Ron Sutton, the prosecutor who won the murder conviction, estimates Jones was responsible for the deaths of 11 to 46 infants in Bexar County from 1978 to 1982, ABC News reported.
Her scheduled release from prison Feb. 24, 2018, after serving less than half her sentence, is the result of a now-expired Texas law that grants "mandatory release" to inmates with good behavior.
Patti McClellan, Chelsea's mother, and others opposed to Jones' release are trying to find another of her alleged victims for a new murder prosecution.
"Just the idea of a serial killer walking free in the United States of America is the craziest thing I have ever heard," McClellan said.