Harare – Zimbabwe’s main opposition, the Movement for Democratic Change (MDC) party has described First Lady Grace Mugabe as a "disgrace", adding that she should have faced justice in South Africa after she severely assaulted a 20 year-old model that she found in the company of one of her sons at a Sandton Hotel.President Robert Mugabe’s wife, who returned to Zimbabwe on Sunday morning together with her husband, was reportedly granted diplomatic immunity by South Africa after she assaulted Gabriella Engels with an extension cord and severely injured her.MDC spokesperson Obert Gutu told News24 that it was regrettable that South African authorities decided not to prosecute the Zimbabwean First Lady after committing such a "heinous crime"."Grace Mugabe is a violent, crude, uncouth and disgraceful character. It is very unfortunate that South Africa decided to grant her diplomatic immunity," said Gutu.'Unacceptable behaviour'Engels was reportedly found with Mugabe’s son, Bellarmine Chatunga, at a hotel in the leafy suburb of Sandton.The Zimbabwean First Lady reportedly assaulted the South African model in the presence of her guards. Engels said she had met Mugabe’s son a day before her assault through a mutual friend. South Africa’s granting of diplomatic immunity to the Zimbabwean First Lady meant that Engels may have to pursue other means to get Grace prosecuted. Engels’ lawyers said they might consider a private prosecution. "Essentially, that woman (Grace) is a bully and a thug who should have faced the full consequences of her act of savagery and violence," added Gutu. Grace, who was reportedly leading a faction of young Turks in Zimbabwe’s ruling Zanu PF party, was reportedly angling to succeed her 93 year-old husband. However, the MDC said the southern African country would be in deep trouble if Zimbabweans allowed her to succeed the nonagenarian.'Sacrificing diplomatic relations'"Grace Mugabe is not presidential material, she is intellectually challenged and morally constrained," said the opposition official. Grace was yet to make a comment regarding the issue.Political analyst Rashweat Mukundu said the assault case damaged the image of the First Lady and Zimbabwe in general.