A prosecutor in the case, Lamido Soron-Dinki, on Thursday asked the judge presiding over the case to close the case of culpable homicide against the girl.
"With a heavy heart, I apply that the accused be discharged," Mr. Soron-Dinki said.
The family of Mr. Sani are said to have forgiven the girl for the deed committed in 2014.
Ms. Tasi'u was married out to Mr. Sani in 2014 as an underage at 14 years.
She allegedly poisoned her husband alongside four others with rat poison out of frustration.
Her case has drawn international attention with calls for her life to be spared.
By Nnenna Ibeh