I was Jane Austen's Best Friend by Cora Harrison

Macmillan, 2010.
(Ages 12+)Highly Recommended. Fifteen year old Jane lies desperately ill at school while the evil headmistress refuses to contact her family. Her orphan cousin, Jenny, also a pupil, fears that Jane will die so risks her life and reputation by creeping out at midnight to send a letter to Jane's parents. She is rescued from grave danger by a mysterious naval captain.
Fortunately Jane and Jenny are saved from their ghastly boarding school and return to Jane's Hampshire home in 1791. What follows is a fascinating insight into Jane Austen's mischievous, sparkling and spirited personality.
Much of the story is told through Jenny's diary and Cora Harrison captures an era where a girl's reputation could be savagely destroyed by a chance encounter and where marriage and money were every mother's preoccupation. There are all sorts of wonderful details about ball gowns, dances, family life and the stifling demands of modesty and decorum that frustrate the young Jane and her cousin.  
The danger and excitement of Jenny's midnight adventure are forgotten, but return to haunt her with dire consequences later in the story.  The fact that Jane has a disabled brother who was banished to live in the village is a source of great anguish to Jane and the cause of her difficult relationship with her mother. While the details in the story might be imagined, Cora Harrison's meticulous research mean that every story line is based on fact, including Jane's disabled brother and Jenny's whirlwind romance with a naval captain.
I was captivated by this story which has all the elements of excitement and mystery while bringing a real person and her era to sparkling life. This is perfect for teenage readers as an introduction to Jane Austen's rich legacy. Highly recommended.
Claire Larson