An aspiring teenage theatre star developed an eating disorder after the "petrified" 15-year-old was groped by former Sydenham resident Rolf Harris, a jury has heard.
Tonya Lee, now 43, who has waived the usual right to anonymity given to alleged sex offence victims, claims that Harris touched her when she travelled to Britain from Australia for the tour in 1986.
She said she lost 9lb-13lb (4kg-6kg) after she "stopped eating" and would "throw up" during the six-week trip. After she returned home, she abandoned her dream of becoming a stage star.
Ms Lee said: " I just wasn't there any more, I lost that passion."
Southwark Crown Court heard that Harris met the performers from the Shopfront Theatre Youth Group when they arrived at London's Heathrow Airport in May that year, and later went for dinner at a pub with them.
Ms Lee had been singing, and said the veteran performer told her she had "a lovely voice" and invited her to sit on his lap.
She said: "I could feel that there was some movement happening beneath me. He was moving back and forth rubbing against me.
"It was very subtle, it wasn't big movements. Everything just seemed to be going on as normal."
The jury of six men and six women was told that Harris started to pat her on the thigh, and then: "He began to move his hand up my inner thigh."
She said she felt "very uncomfortable" as Harris touched her genitals over her clothing, and she "started to panic" before rushing off to the toilet.
"I was wondering what to do, 'How can I get out of this?', and also I was confused. The whole time this was happening just normal interaction was going on," she told the court.
Ms Lee decided not to tell anyone because the group's artistic director, Kathy Henkel, was friends with Harris, and she felt confused.
When she came out of the toilet, Harris was waiting outside, the jury heard.
The alleged victim said: "He came up and I don't know the exact words but it was something like 'I just want to chat to you some more'.
"I was intimidated because I felt quite claustrophobic."
Harris got her in "a big bear hug", and put his hand down her top and fondled her breast, it is claimed.
Ms Lee said: "I was petrified... I was in shock."
She added: "I felt stuck. I felt like I couldn't move. I was petrified, I froze."
Harris then touched her intimately, it is claimed.
Ms Lee said: "I just wanted to burst into tears at that stage, and I just wanted to run."
She added: "I was gobsmacked, I was shocked. Completely in disbelief."
Harris is accused of 12 counts of indecent assault between 1968 and 1986, all of which he denies. Three of the charges relate to Ms Lee's claims.
She said after the alleged assault she rushed back into the toilet.
"I was quite emotional, so many thoughts were running through my head. I couldn't believe what had happened. I felt disgusting. I did not know who to talk to."
Ms Lee said she thought no-one would believe her "because it was Rolf Harris", and that she became "an empty vessel" after the alleged abuse.
"I was wondering why I was picked out of all those other people," she said.
She decided not to tell her "protective" mother, because she had pushed for permission to go on the trip.
Earlier, Ms Lee had told the court: "She was very hesitant to let me go. She had always been quite a protective mother."
She added: "I just convinced her that I'd be safe and I'd be in good hands."