Molly-Mae Wotherspoon, aged six months, was attacked at her mother Claire Riley's home, by an American pit bull on 3 October last year. She died later in hospital.
Ms Riley, 22, of Daventry is accused of being the owner of a dangerously out of control dog resulting in a death.
Susan Aucott, 54, of Kettering, has been charged with the same offence.
An inquest heard Molly-Mae died of blood loss from head wounds.
The coroner said the family had "paid the ultimate price" for having an illegal breed of dog.
The animal, prohibited under the 1991 Dangerous Dogs Act, was destroyed.
Supt Andy Cox, head of the county's operational command unit, said: "These incidents are extremely rare and it is the first time in Northamptonshire that someone has been charged with this offence.
"It took some careful consideration from experts within CPS to come up with the final decision."
Both women were charged under dangerous dogs legislation, with being the owner or person in charge of a dog, dangerously out of control, that caused injury to Molly-Mae resulting in her death.
They have been released on bail and are due before Northampton Magistrates' Court on 21 September.
The mother and grandmother of a baby killed by a banned breed dog have been charged in connection with her death.