The family was speaking at a press conference on Thursday held by civil rights group, Afriforum, which is now representing 20-year-old Gabriella Engels.
Former star prosecutor, advocate Gerrie Nel, has taken up the case.
“I was very impressed by the family saying for them it’s not about money, it’s not about paying an amount of money, receiving an amount of money so that they case would go away.
"For them, it’s about justice and that impressed me because that is why we created this office: to ensure that justice is done and to ensure that they are no selective prosecutions. So certainly it impressed me that the family said they’re not interested at all,” Nel said.
Engels laid a charge of assault against Grace Mugabe, who allegedly attacked and beat her using an extension cord.
The model and her friends were at a hotel in Sandton on Sunday night when the incident happened.
Grace Mugabe initially agreed to hand herself over to police earlier this week, but was a no-show, and has now invoked diplomatic immunity to avoid prosecution.
Police however issued a "red alert" to prevent her from leaving the country.
Her husband, President Robert Mugabe, arrived in South Africa two days early for the SADC summit, fuelling speculation he did so to ensure his wife's diplomatic immunity.