Ms Muchiriwesi had not hired a maid without some checks.
An acquaintance of hers had brought Billiat round and claimed she was her sister. But when Ms Muchiriwesi confronted her later the acquaintance denied all knowledge of the teenager and revealed, now it was too late, that they had met in the street.
Harare magistrate Mr Clever Tsikwa, who heard the case, sentenced Billiat to 48 months of which 20 were suspended on condition she does not commit a similar offence within five years.
In passing the sentence, Mr Tsikwa considered that Billiat deprived the boy of freedom and both the mother and the child were traumatised with their four-month separation.
"There are no allegations that she ill-treated the child," said Mr Tsikwa.
But kidnapping, the magistrate noted, remained a serious offence and an act of brutality.
"I considered leniency in passing the sentence but it must not be taken too far for the sake of justice," said Mr Tsikwa.
Prosecutor Ms Tapiwa Joyce Fusire wanted a far stiffer penalty saying Billiat's moral blameworthiness was very high.
"She deprived the minor from his mother's affection, support and he was removed from the environment he was used to and in the process the boy was plunged into an identity crisis.
"When parents leave their children with maids they intend to leave them in safe hands and expect to see them in good health when they return home. If it was not her intention (to keep the child forever) she could have called the complainant demanding a ransom," Ms Fusire said.
And Ms Muchiriwesi, what is her last word?
"I almost gave up hope. I thought the boy was dead. But something kept telling me to keep phoning the maid's number, and at last I got through.
"When she returned my call I was very happy. Initially I wanted to go alone and pay the ransom, but then decided to tell the police." And the police were able at last to act.