Nicola Priest, 22, claimed Callum Redfern, 21, hit her three-year-old daughter Kaylee-Jayde hard enough to make her cry, Birmingham Crown Court was told.
Both Priest and Redfern, the latter who is from Dudley, are charged with a number of offences in relation to the death of Kaylee-Jayde, including murder and cruelty to a child.
Kaylee-Jayde died from serious chest and abdominal injuries in August last year at her mother's flat in Solihull.
Medical examinations revealed she had also suffered historical injuries including broken ribs, lower leg fractures and a broken sternum.
In cross-examination by her defence counsel Carter-Stephenson at court, Priest said Redfern used physical force to discipline her child.
She said: "He would raise his hand back and smack her. It was quite a hard smack."
Asked if her daughter would cry, she said: "Yes. I would hug her and tell her I loved her. She would say 'mommy' but nothing else."
Priest said she reacted by telling Redfern that her child was "only three and didn't understand".
She said she was not happy about Redfern "disciplining" her child but did not try to stop him.
Asked why, Priest said: "I was scared. My thoughts were what if he starts to hurt me.
"He said I am not disciplining her enough. It never crossed my mind [he might be causing injuries to Kaylee-Jayde]."
If her child misbehaved, Priest said she would put her to bed for three minutes.
She said that Redfern's actions did not influence the way she treated Kaylee-Jayde when discipling her.
"I still continued to put her to bed for three minutes, although I have smacked her," she said.
"[I would smack her] sometimes on the hand and sometimes on the bum. I would never leave a mark or make her cry."
The court heard Redfern would help put the three-year-old to bed on occasions when visiting Priest's home.
When Redfern gave evidence, he told jurors he never smacked Kaylee-Jayde.
Redfern, 21, of Temple Street, Dudley, and Priest, 22, of Poplar Avenue, Edgbaston, deny murder, a separate alternative charge of manslaughter and a charge of causing or allowing the death of a child and cruelty to a child, between June 12 and August 3, 2020.
The trial continues.