Police say Ms Esther Wanjiru, 95, was secretly buried at Ndomba village in a shallow grave which was then covered with dry grass.
Police have gone to court seeking an order to have the body exhumed.
Visit younger sister
Two family members have also been picked up and are helping the police with investigations.
According to neighbours, Ms Wanjiru left her home last month to visit her younger sister at Kiandegwa village as her health was deteriorating. She stayed with her sister for two weeks and then returned to her home in Ndomba.
The residents said family members disagreed on who should take care of the sickly woman and a quarrel ensued. â€œThis woman was seen as a bother and no one wanted to stay with her,â€ one of the villagers said.
After tempers cooled down, Ms Wanjiru who walked with difficulty due to her advanced age, was on Sunday left on her own in the homestead.
It was then that unknown people allegedly dug a grave at 11pm and threw her in it. They covered the grave with soil and then placed dry grass on it and went away unnoticed.
Ms Wanjiruâ€™s sister went to visit her the following day only to find her missing. Her family members did not have definite answers as to her whereabouts.
Some said she had been admitted to hospital. The sister became suspicious and went and reported the situation to area chief Nancy Gichuki.
When she visited the home, she was shown a fresh grave after which she called in the police to carry out investigations.
Ms Gichuki said it emerged that the woman was buried without anyoneâ€™s knowledge, which raised suspicion.
â€œThe information I received was that the woman was secretly buried at night. Those who did that never reported to the authorities that someone was dead as required by the law. There is something amiss,â€ she said.