Speaking to reporters on 2 February, Dariga Nazarbaeva also said the KNB's elite unit, Arystan (Lion), should be disbanded.
The call came one day after the KNB said five members of Arystan had been arrested in connection with the murder of the opposition leader Altynbek Sarsenbaev.
Arystan reports directly to the head of the KNB, Nartay Dutbaev.
The body of Sarsenbaev, the co-chair of the Naghyz Ak Zhol (True Bright Path) party, was found on 13 February together with the bodies of his bodyguard and driver. They had been shot.
Opposition figures suspect the authorities had a role in the killing. The Kazakh government denies this.
Dariga Nazarbaeva is a powerful player on the Kazakh political scene. She is a member of parliament and heads her own party, Asar (All Together).