Why was the landlady trembling in "Cry the Beloved Country"?

Although she claims that the reason she is trembling is because she is cold, the landlady, Mrs. Mkize, is actually trembling because she is afraid. 

Mrs. Mkize had housed Absalom Kumalo and his cousin John for awhile about a year ago.  While they were there, they engaged in illegal activities, probably some sort of theft.  Mrs. Mkize finally admits that "they brought many things here...in the late hours of the night.  They were clothes, and watches, and money, and food in bottles, and many other things".  Mrs. Mkize is afraid when Stephen Kumalo and his friend Msimangu show up at her door asking about her former lodgers because she thinks the two priests may be working for the police and she does not want to be implicated in the activities of Absalom and John Kumalo.  It is only after Msimangu swears on the Bible that he only wants to help a father who is seeking his son that she reluctantly gives him the information for which he is asking (Chapter 8). 

The novel is set in South Africa in the years after World War II.  Issues of apartheid and economic desperation are the defining orders of the day, and an atmosphere of lawlessness and suspicion pervades relations among blacks and whites alike.  It is not surprising that Mrs. Mkize is reluctant to impart information that may get her in trouble with the law.