In a statement, the Ministry of Police said these discussions are "to make sure that the suspect is processed through the legal system".
On Wednesday, she instead sought immunity from.
A spokesman for the Department of International Relations and Cooperation, Clayson Monyela, told The Associated Press that the bid for immunity was under consideration.
President Mugabe, speaking during a recent party rally in Gwanda, in Zimbabwe's Matabeleland Province, said his wife had gone to South Africa for a medical consultation over her leg, which had been injured in a freak accident.
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Earlier, South African police had been negotiating with Grace's lawyers to get her to turn herself in to face charges of assault in a court room, a senior police source said.
The police said the Zimbabwean government asked for diplomatic immunity for a suspect involved in the alleged assault.
In a statement released by the police, Naidoo said: "Since yesterday‚ it has emerged on several media and social media platforms that a 20-year-old South African woman was allegedly assaulted by a prominent woman at a hotel in Sandton".
There was no immediate public comment on the case from Grace, 52, a possible successor to her husband President Robert Mugabe, 93, who has ruled Zimbabwe since 1980.
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The model told independent media in South Africa that she fears being victimized for telling it all, noting that she now spends most of her time at home.
Mbalula needs to do his job and ensure she is arrested and has her day in court to answer the serious charges against her.
"She split my head open in three places with an extension cord and used the plug to hit me", 20-year-old Gabriella Engels said.
"Rob jnr was put out of the hotel room and Bellermine ran away".
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Mugabe has been accused of assaults during other overseas trips, including a 2009 visit to Hong Kong in which a photographer accused her of beating him up.