Crown solicitor Mike Smith said while the mother did not blow cannabis on the baby's face, she was nonetheless a party to the act by allowing it to occur when the toddler was in her care.
He said the Crown was not required to prove the offence was committed by her or someone else, but that it happened in her care which was a departure from the standard of care expected of her.
Smith said she minimised her offending and shifted the blame on to others.
Defence lawyer Wayne McKean said an analysis of evidence showed it was her partner who was violent towards the baby, that he was a large man, and was a possible cause of unexplained injuries on the toddler.
The baby was healthy and well looked-after when checked by Plunket at 3 months old, he said.
McKean said the bruising on the baby's forehead was likely to have been caused by knocking on his head with knuckles and the injury on his ribs could have been as a result of punching and squeezing him - acts her partner did.
The fractured skull was caused by him hitting his head against an object such as a game console or something protruding from a wall with a flat edge.
On the thumb fracture, McKean said the pathologist didn't see it and the Crown did not call the radiologist who analysed x-ray results.
Her partner allegedly blew cannabis over the baby's face and gave him alcohol but it wasn't clear how much was given, he submitted.
The mother told the court on Monday she would take her baby away from her partner when the latter become "rough" and the 5-month-old would cry.
She saw her partner squeezing the baby with his knuckles on both sides of his ribs and on top of his head, and slap him on his forehead and mainly around the back of his head.
On one occasion, she said the baby's father allegedly held the baby then dropped him on to the carpet in the lounge which resulted in the child fainting.
Justice van Bohemen will deliver his ruling on February 26.
