HARARE (AFP) - Zimbabwe's first lady Grace Mugabe appeared in public for the first time on Friday (Aug 25) since she returned from South Africa where she was accused of assaulting a model and granted diplomatic immunity.

The wife of President Robert Mugabe allegedly attacked 20-year-old model Gabriella Engels with an electrical extension cord at an upmarket hotel in Johannesburg where the couple's two sons were staying.

Grace Mugabe appeared at the Harare annual agricultural fair, smiling and stopping to chat with exhibitors as she toured stands alongside her husband, an AFP correspondent witnessed.

The first lady, who is seen as possible successor to her 93-year-old husband, was granted diplomatic immunity by South Africa at the weekend and flew out of the country.

Engels suffered cuts to her forehead and the back of her head during the alleged Aug 13 assault.

She has opened a police case alleging assault with intent to do grievous bodily harm.

Engels' lawyers this week filed a court injunction to try to annul the government decision to grant Grace Mugabe diplomatic immunity.

South Africa's main opposition, the Democratic Alliance, has also approached the courts asking it to declare the immunity "wholly without legal merit" and "unconstitutional".

The party is arguing that Grace Mugabe is not a member of the Zimbabwean government and was visiting South Africa on personal business.

"There is nothing in either South African or international law which renders her deserving of diplomatic immunity," the DA said in a statement.

In 2009, Grace Mugabe was granted immunity in Hong Kong after repeatedly punching a British photographer for taking pictures of her at a luxury hotel.