She then took the body to Karatina Hospital mortuary where she told attendants he had died after falling sick.
When the area assistant chief heard of the act, she arrested the woman and handed her to officers at Baricho Police Station.
Area police boss Mohammed Huka said the woman was being questioned.
A woman shocked police on Thursday when she confessed to sacrificing her son to the devil.
The woman was picked up on Tuesday in Kirinyaga after it was claimed she strangled her eight-year-old son on Monday night and offered him as a sacrifice.
“She has confessed to sacrificing her son to the devil,” he said. “She told us she is a member of a cult that worships the devil and, when commanded to sacrifice a member of her family, she chose her son,” said Mr Huka. “She claimed she had no option.”
Mr Huka said the matter was being treated as murder.
“Murder charges will be preferred against the woman once we are through with investigations,” he said.
The police also want to establish whether the woman, who lived quietly in the village, is of sound mind or not.
As news of the alleged human sacrifice spread, villagers demonstrated and threatened to lynch the woman.
“Human sacrifice to the devil is unheard of in this village and we are really shocked,” said Mr John Ngure.
The villagers demanded that the woman should never return to the village.
“She may be commanded to sacrifice more people from our village and we are not going to wait until that happens,” another villager, Mr Stephen Muriuki, said.
The villagers also demanded that the woman reveals her fellow worshippers and the cult’s leader.