Grace Mugabe's return home after being granted diplomatic immunity felt like a slap in the face for the family of Gabriella Engels, who was allegedly beaten by Zimbabwe's plug-wielding first lady.

President Robert Mugabe and his wife flew out of South Africa in the early hours of Sunday morning after a week of public outrage and diplomatic wrangling - untouched by the authorities after Engels, 20, laid a charge of assault with intent to do grievous bodily harm against her after an altercation at a hotel in Sandton, Johannesburg.

"I'm not surprised at all. I knew the government was going to disappoint me," Engels told The Times. "I'm upset. But this is definitely not the end of my case," she said on Sunday.