Katie Crowder deliberately hurt 19-month-old Gracie at their home in Mansfield in March and delayed getting help, Nottingham Crown Court heard.
Prosecutors said Gracie suffered burns that covered 65% of her body and was left for at least an hour.
Her severe injuries could not have been caused accidentally, they added.
Crowder, 26, of Wharmby Avenue, denied murdering Gracie on 6 March but was found guilty earlier this month following a trial.
She was ordered to serve at least 21 years in prison on Wednesday.
Judge Jeremy Baker, sentencing, said: “What happened to Gracie on that Friday morning is as distressing as it is tragic.
“It is apparent from the jury’s verdict that you poured a significant quantity of scalding water on Gracie’s face and body.
“Death would not have occurred swiftly and she would have continued to suffer pain and distress for a significant period of an hour or more.”