Roxanne Davis, of Lee Road, Gosport, Hampshire, is on trial at Winchester Crown Court accused of causing or allowing the death of Stanley Davis.
The 30-year-old is accused alongside her ex-partner Samuel Davies, 24, of Mayfield Road, Southampton.
The court has heard that the baby died of a skull fracture and brain haemorrhage at just 24-days-old on March 28, 2017.
He had also suffered 32 fractures to his ribs and nine fractures to his arms and legs sustained during three separate occasions.
Davis told the court that when her son was born she was "over the moon" and added: "I had my whole world in my hands."
She said her mental health was "amazing" with her son and added: "Stanley took it all away."
She admitted having arguments with Davies during which she had thrown things around in their flat including an ornament belonging to her co-defendant, a metal baby bottle steriliser and a bottle of Coke.
She also accepted she used "disgusting" language in text messages between them.
She said that accusations against Davies in her messages calling him a "wife-beater" were "just words because I was angry".
Davis said he had not "beaten her" only "grabbed" her to prevent her from leaving.
She added: "I have never punched him, I do not think he would let me get away with it so I never hit him in the face, I think I have slapped him and a few things."
Davis denied that she had hurt Stanley and said: "I didn't, I wouldn't lay a finger on him."
She said at first she had suspected other family members of accidentally hurting her son.
She said: "I did at first, thought someone was holding him wrong and they hurt his head by accident and they didn't tell me."
Davis added that she did not know who had hurt Stanley and said she had not seen Davies lose his temper with him and had not thought he was a danger to the child.
She added: "I thought he loved him."
The defendants, who share similar surnames but are not married, both deny the charge and the trial continues.