She, her father Alfred and his fiancee, had just ordered lunch when a bomb exploded, killing one person and injuring 66.
Clementson, now aged 24, said she could not hold down a job or form a romantic relationship because of the psychological scars and trauma she suffered.
Clementson and Vic Serrano - whose daughter Marryanne was killed in the blast - on Tuesday opposed the amnesty application of four former Umkhonto weSizwe cadres who have taken responsibility for the attack.
Elfus Ndlovhu, Tebogo Kebothlale, Molwedi Mokwena and Ernest Sigasa, who headed the Johannes Nkosi unit, are applying for amnesty.
Clementson and Serrano told a Truth and Reconciliation Commission amnesty hearing on Tuesday that the attack was not politically motivated because Ndlovhu, who admitted to having planted the limpet mine, had earlier said he did not see any member of the security branch in the restaurant when he executed the plan.
Clementson related the event: "It was at about 11.45am, I was seated with my dad and his fiancee. We had just placed our order and, seconds later, the electricity went off. I felt as if I was being electrocuted.
"Someone shouted that there must have been another bomb. There was blood everywhere and everybody running away, trampling on each other. There was fire and the roof was falling. It was absolute chaos," Clementson said.
"I cannot forgive or forget because my whole life has been ruined. I cannot bear children, I cannot work and I cannot keep a relationship.
"I have nightmares and I can still lose my leg because of the injuries," she said, adding that she had been undergoing surgery since the incident.
Serrano said the applicants should have blown up a police station if they were targeting members of the security branch.
"I cannot forgive because my daughter was killed for nothing. People were maimed for nothing and there was no purpose.
"That bomb could have been placed at the police kiosk which was nearby. Attacking a place where young people kill time is like killing the future of the nation," Serrano said.
Committee chairman Judge Ronnie Pillay requested Brian Koopedi, counsel for the applicants, to forward a written motivation for the amnesty application.