Frances Wilson (Faber, £18.99)

Dorothy Wordsworth, beloved sister of William, has been described as "probably the most remarkable and the most distinguished of English prose writers who never wrote a line for the general public". The best known of her writing appears in four small notebooks that have become known as the Grasmere Journals, which covered a period of two and a half years.

But she was also a prolific letter-writer and diary-keeper throughout most of her life, as well as amanuensis for her brother, who hated the actual act of writing. She even wrote his love letters for him.

A rich seam, indeed, for a biographer. And, in The Ballad of Dorothy Wordsworth, Frances Wilson has given us a full account of this extraordinary woman, whose relationship with her brother has never been truly ascertained.

She certainly exhibited deep sisterly devotion, but behaved like a rejected mistress on the morning of his wedding, having a strange collapse and being unable to attend the ceremony. (And she went on honeymoon with the newly-weds.) Dorothy Wordsworth was tiny, lost her teeth by the age of 40 and became wild and neurotic - descending into a sort of madness in her later years.

Thomas De Quincey described her as "the very wildest... person I have ever known". Yet she ran a very orderly household, and her journals are full of delightful domestic detail - putting cold mutton into William's pockets before he sets off for a walk, baking pies, interminable headaches - as well as appreciative descriptions of their glorious surroundings.

Wilson gives us all this, and far more, in a true biography, bringing Dorothy to life in her own right. The book makes extensive and judicious use of Dorothy's letters and journals, whose extracts Wilson intersperses seamlessly with her own narrative. And, as in Dorothy's own writings, we have a delightful mixture of mutton and moonscapes, puddings and perambulations, friendships and frosty mornings. It is all woven together into a fluent, fascinating, fulsome picture of this complex woman, who was muse and inspiration for two of our finest poets - Wordsworth and their great friend Coleridge.

Frances Wilson will be at the Oxford Literary Festival on April 1.