The Directorate of Criminal Investigations said after the arrest of Chania on Friday that she is believed to have mooted the murder plan after she learnt about her husband's alleged love affair with a secretary at a local school.
Until his death, Mwangi was a contractor based in Rwanda and had arrived in the country on September 13.
The couple had been married for 20 years with three children.
The 58-year-old engineer's body was dumped at Kieni Forest near Kamunyaka village, along the Thika-Magumu highway.
Police said Chania identified Mwangi at the morgue days after she reported him missing at Mwea and Gachege police posts in Gatundu North respectively.
Detectives believe the man was killed elsewhere and dumped near the forest. The body was wrapped in black polythene and stuffed in a bag, from which blood oozed.
In the last General Election, Chania vied unsuccessfully for the Kiambu Woman Representative position on a Jubilee Party ticket.
In 2017, Chania also lost the Woman Rep position to current Githunguri MP, Gathoni Wamuchomba.