She has just finished a book for adults with poor reading skills, as one of 22 best-selling authors who have been commissioned to write books containing words with no more than two syllables for adults with reading difficulties.
"I may have been writing in simple language but I was writing for grown-ups," she said. "Sentences were short and paragraphs were short. I found the limitations frustrating."
Her book, The Thief, will be published on World Book Day in March next year along with 11 others by writers including Joanna Trollope, Maeve Binchy, and Richard Branson. Ten more books in the Quick Reads series will be published during Adult Learners' Week in May, with authors including Hunter Davis and Andy McNab.
Baroness Rendell, speaking at a Skills for Life dinner organised by Business in the Community, said the books are designed for adults who can read simple words and need to improve.
Most books written for this level of reader are children's books, so the big-name writers were invited to write in a simple style with adults in mind.
Julia Strong, director of the National Reading Campaign, said: "There has been such a shortage of good reads for emergent readers so it's wonderful to see the publishing world working with the adult literacy community to fill this gap."
Each Quick Read book will cost pound;2.99.
Colleges and adult learner centres will be distributing up to five million pound;1 vouchers to those on basic skills adult literacy courses, which can be spent on any of the Quick Read titles.