She told the jury she was raped on two different occasions in 1967, when she was 15, at the actor's then home in Lancashire.
Preston Crown Court was told the woman only came forward to police last year in the wake of a number of celebrity sex scandals.
In her police interview played to the court, the woman told a female officer: "All these years I have never brought it to anyone's attention. I chose not to say anything.
"I thought I was to blame, especially the second time.
"I was gullible ... I was a kid. I would never have repeated it to anyone."
But by last year she said "it has started to bother me because there might be other people that this has happened to".
The woman detailed how in the first alleged assault Roache - whom she said she knew - had sex with her with "no warning" in the bedroom of his bungalow.
"I was a bit shocked," she said. "There was no warning to anything that would have happened.
"There was nothing to suggest that anything improper was going to happen.
"It happened before I realised it. I didn't know what to do. I was panicking."
She added: "I thought it was my fault and I didn't know why because nothing had taken place before that suggested that anything was going to happen."
The woman said she was raped again later in the year when he again invited her into his home.
"Before I knew it I had been grabbed again," she said.
She said she should not have gone in his home the second time.
The complainant said she did not see him again until years later when she was a young mother.
He walked past at her at a local carnival and said: "Oh hello, I know you don't I?"
She said that was the last time she had seen the actor.
Opening her cross-examination, Louise Blackwell QC, defending, told the witness: "All the questions I am putting to you are on the basis that neither of these events happened, just so you understand."
She then proceeded to question her about the layout of Roache's former home.
Roache, 81, of Wilmslow, Cheshire, denies five historic counts of indecent assault and two historic counts of rape involving the complainants who were aged 16 and under.
The offences are said to have occurred between 1965 and 1971.
The trial continues.