June Steenkamp has said she will be in court for the appeal against Oscar Pistorius's manslaughter conviction for killing her daughter Reeva.
At the hearing in South Africa on Monday, the state will argue that the trial judge misinterpreted parts of the law and ignored vital evidence.
A panel of five judges could then choose to convict Pistorius of murder, order a retrial or reject the prosecution's appeal.
Pistorius left prison last week to serve his remaining sentence under house arrest.
June Steenkamp has said she will be in court to support those fighting his conviction.
“Nothing is going to bring my daughter back and I have no feelings of revenge or wanting bad things for him, I am not like that, I am actually going to the re-trial on Monday,” Ms Steenkamp said.
“I wasn’t going to go, but I have decided that I must support the people who are fighting for the justice for her.”