Tonya Lee, 43, who has waived the usual right to anonymity given to alleged sex offence victims, claims Harris touched her after she travelled in 1986.
Harris met the group when they landed at Heathrow Airport, London, and later went for dinner at a pub with them.
Ms Lee, then 15, said she was invited to sit on the entertainer's lap, and that his hand began to creep up her thigh.
The jury at Southwark Crown Court, London, was told Harris started to pat her on the thigh, and then touched her intimately over her clothing.
Ms Lee said Harris continued "laughing" with other people while touching her. She said she went to the toilet and when she came out Harris was waiting outside.
Ms Lee said Harris got her in "a big bear hug", and put his hand down her top and fondled her breast.
Ms Lee said: "I was petrified ... I was in shock."
Harris then touched her intimately, the court heard.
Ms Lee said: "I just wanted to burst into tears at that stage, and just wanted to run."
The court heard the mother-of-three later agreed to sell her story about the alleged abuse for £33,000 to a magazine and TV show - but claims she has only received £15,400.
Ms Lee said she was plunged into decades of emotional turmoil by the abuse she claims to have suffered at Harris's hands.
She said she almost killed herself by taking a potentially lethal mix of dozens of laxatives a day while drinking heavily and half-starving herself because of her eating disorder.
Harris, 84, is accused of 12 counts of indecent assault between 1968 and 1986, all of which he denies.
The trial continues.