Roberts died at the scene but Gacitua was uninjured.
Linda Brown, a 49-year-old receptionist, said she and her husband were heading home to East Tamaki Heights when they were hit head on.
"We were very lucky not to be seriously hurt but we were both admitted to hospital and I had a lot of bruising," she said. "This girl lost her life. It's such a senseless, stupid thing."
Fay's father, Harvey Roberts, said his daughter was a talented hairdresser who ran a salon with her mother, Karen, in East Tamaki Heights.
"It is very difficult for my wife. She has to face working in that environment every day. Clients are still coming in and asking for Fay, not realising she is gone. Her voice is still on the answerphone. Her name is all over our PC. So the day-to-day is still very difficult," he said.
The family moved to New Zealand from England 11 years ago. Fay's younger sister Ruby, 15, and her brother Sam, 23, have been distressed and angry since her death.
Fay's father declined to talk about his feelings towards Gacitua. "He will have to go through due process," he said.
Constable Andrew Petrie, of the Serious Crash Unit, said charges had been laid following scene examinations and interviews with witnesses.
Gacitua did not return a request for comment but his sister said he was devastated by Fay's death. "She was part of our family ... she was my best friend," she said.
Gacitua has been remanded on bail to reappear in the Manukau District Court on October 26 and Matthews has been remanded to November 15.
