In December 1804 as JA celebrated her 29th birthday in Bath, her friend Mrs Lefroy met with a fatal accident while out riding her horse in Hampshire.

Look at this account of the sad incident from A Family Record by Dierdre Le Faye:

….on that same day in Hampshire Madam Lefroy rode out from Ashe Rectory, accompanied as usual by her servant, to shop in Overton. She met James Austen in the town, and observed to him that the horse she was riding was so stupid and lazy she could scarcely make him canter.

My father rode homeward, she staying to do some errands in Overton; next morning the news of her death reached Steventon. After getting to the top of Overton Hill, the horse seemed to be running away - it was not known whether anything had frightened him - the servant, unwisely, rode up to catch the bridle rein - missed his hold and the animal darted off faster. He could not give any clear account, but it was supposed that Mrs Lefroy in her terror, threw herself off, and fell heavily on the hard ground. She never spoke afterwards, and she died in a few hours.

and on 21 December James buried her.

Jane's immediate reaction to the tragic news is unknown, but on the anniversary four years later she wrote her longest and most serious set of verses in memory of this dear friend of childhood days, still grieving bitterly at her loss. A Family Record page 145

A little over a month later a further death devastated her family group: Mr Austen died on the 20th January 1805 at Green Park Buildings.