The tot fell unconscious but despite having contact with the girl’s mother, Klein failed to seek medical help.
She finally called emergency services a day after the attack and Alaya was taken to hospital in Niagara Falls, New York, WIVB reports.
Alaya was diagnosed with a bleed on the brain, a fractured skull and spinal cord damage.
Despite best efforts from medics, she died from her injuries in hospital.
Neither the state’s prosecutor or Klein’s defence lawyer has given a motive for the attack, according to the Niagara Gazette.
Assistant District Attorney Holly Sloma said: "Everyone wants to know, why did she hurt her and why didn't she seek help.
"She did this to a defenseless baby, and she did nothing — nothing — to seek help.”
The child’s heartbroken grandmother Crystal Dusen said Alaya never got to meet her father.
Ms Dusen said: “She'll never get to smile or laugh, and her mother will never see her again."
Klein initially denied any wrong doing before pleading guilty to first-degree manslaughter on October 15.
She was sentenced to 25 years in prison – the maximum jail term possible for the charge of first-degree manslaughter.
Klein was also jailed for seven years for a robbery charge and 30 months for a drug charge. The two additional sentences will run concurrently.
