Nyanza police chief Joseph ole Tito said the suspect was arrested while heading to the Malaba border on Monday morning.
The woman is accused of stealing the pistol while she was having a drink with the officer last week.
“During his stay here in Kisumu, he happened to have lost a firearm and so in that process we started looking into it and it became apparent that the officer had a lady friend with whom he had shared a drink,” Tito said.
“When he realised he had lost his firearm one of his suspects became the lady and we ended up arresting her,” he added.
The police officer has already appeared in court charged with failing to safeguard the firearm and ammunition entrusted to him.
David Okinda was charged before Senior Principal Magistrate Samuel Atonga for failing to keep safe custody of the Ceska Pistol loaded with 15 rounds of ammunition.
He denied the allegations and was released on a bond of Sh100,000 or a cash bail of Sh50,000.
The woman will be charged in court on Tuesday while Okinda’s case will be heard on May 17.
Cases of police officers losing their firearms are not uncommon in Kenya. Most cases lead to interdiction or dismissal depending on the circumstances.
Odinga’s and former Vice President Kalonzo Musyoka’s security was significantly cut down after the new government took over.
The Jubilee government has however pledged to work out a security arrangement that will increase the number of officers assigned to offer them VIP protection.
Odinga and Musyoka’s previous security detail had about 20 officers at any given time.