Sarah Rimmer was the cousin of Arnold Rimmer.
She was the daughter of Arnold's uncle Frank, his father's brother. Sarah and her twin sister Alice were two years older than Arnold, and were very attractive with blond hair.
When Arnold was fourteen, he and his mother went on holiday with Frank, Sarah and Alice. Arnold had managed to convince himself that his sixteen year old cousin Sarah fancied him, but he wasn't sure about Alice. He was pleasantly surprised to wake up in the night with a tongue down his throat, only to discover it was neither Sarah nor Alice but his uncle, who had been looking for his sister-in-law (RD: The Last Day).