We all know that Cassandra was not only Jane's sister but her best friend. It is because of the letters Jane wrote to her sister that we know so much about our beloved author.
In 1794, Cassandra became engaged to Thomas Fowle. Fowle needed money to marry and went to the Caribbean where he died of yellow fever in 1797. Cassandra inherited £1000 from him, which gave her a little financial independence but, like her sister, she never married.
Cassandra is reported to have destroyed two thirds of Jane's letters in 1843. After the death of her mother, Cassandra lived on alone at the Chawton cottage but continued to visit friends and relations. On one such visit to her brother Frank in March 1845, she suffered a stroke. She died there a few days later on 22 March 1845, aged 72. Her body was returned to her home village of Chawton for burial at St. Nicholas' Church alongside her mother.
Cassandra Austen: Jane Austen's Beloved Older Sister - JaneAusten.co.uk
The Closeness of Sisters: Imagining Cassandra and Jane by Juliette Wells - Persuasions On-Line V. 30, NO.1 (Winter 2009)
Cassandra Austen: Jane's confidante, supporter and helpmate - Jane Austen's World
*note: Source material Cassandra Austen - Wikipedia