Benjamin Herman, 80, of Hook, Hampshire, denies four counts of sex abuse against a girl under 13 in the early 1970s.
Mr Herman is a former equerry to the Duke of Edinburgh.
Under cross-examination, the woman told Blackfriars Crown Court: "I am not fantasising, lying or imagining it."
Mr Herman held the equerry post between 1971 and 1974, managing the duke's official diary and accompanying him on official visits.
He faces three counts of indecent assault on a girl under the age of 13 and one count of indecency with a child between January 1972 and January 1974.
The court heard the woman wrote in a letter to her brother last year: "He groomed and manipulated me and assaulted me four or five times."
Defence counsel Nerida Harford-Bell accused her of making up "lies", hating "posh people" and hunting for attention.
She also suggesting the woman was "hoping to get money from this".
The woman told the court: "I don't want any money, I don't want his wretched money. I don't want anybody's money."
Members of Mr Herman's family in the public gallery wept as the exchange took place.
The trial continues.
A woman who claims she was "groomed" and sexually abused by a former royal aide told a jury she had not made up the story and did not "want his money".