Giving evidence at Southwark Crown Court, the woman, who cannot be named for legal reasons, said she met the entertainer while on holiday in Malta in 1970.
Her boyfriend hurt his foot while swimming, and Harris, now 84, came out of a bar and helped them find a doctor, the jury was told.
The woman then went back to thank the artist, and he took her into a side room, offering to show the aspiring art student some of his work.
It is claimed he pinned her against a wall and gave her a "slobbery" kiss before touching her intimately.
The woman said of the kiss: "It was quite slobbery. It wasn't very nice.
"I was quite shocked, more shocked than anything."
She told the jury at first she was "a bit flattered", and that after the alleged assault Harris "just stopped whatever he was doing and just cuddled me".
Prosecutor Sasha Wass QC asked her: "Did he say anything?"
She replied: "(He said) 'I'm sorry'."
The woman said she was "just in shock really, happy that was it. I thought I was going to be raped. I don't know what I thought really."
Afterwards the pair went back to the bar, where the woman told the court she had her photograph taken with Harris.
She said the entertainer squeezed her arm "really tight" as the picture was taken.
"It was as if it was an apology," the woman said.
The alleged victim is not named on the indictment because the claimed incident happened abroad before such crimes could be prosecuted in the UK, but has been called as a prosecution witness.
Harris, from Bray in Berkshire, is accused of 12 counts of indecent assault on four alleged victims between 1968 and 1986, all of which he denies.
He listened from the glass-walled dock, with wife Alwen and other family members including his niece and brother-in-law watching from the public gallery.
The court also heard from two other women who are supporting prosecution witnesses and were flown over from Australia and New Zealand to give evidence.
The first of these women told the jury of six men and six women that when she was 11-years-old, she was at a family friend's home in Australia in 1969 while she was off sick from school, and came downstairs in her pyjamas and saw Harris, the court heard.
The woman said: "When I came down the stairs he asked me how old I was, and he said 'good, I want to be the first one to introduce you to a tongue kiss'.
The trial was adjourned until today.