Jane Austen completed six full-length novels in her lifetime: six.
Those novels are Sense and Sensibility, Pride and Prejudice, Mansfield Park, Emma, Northanger Abbey, and Persuasion. Four appeared while Austen was alive: Sense and Sensibility in 1811, Pride and Prejudice in 1813, Mansfield Park in 1814, and Emma in 1815. Northanger Abbey and Persuasion were published together after her death in 1817.
The wording “completed in her lifetime” matters because Austen also wrote unfinished fiction. The Watsons was abandoned, and Sanditon remained incomplete when she died. She also produced juvenilia, letters, poems, and the short epistolary novel Lady Susan, but these are not normally counted among her six major novels.
Readers sometimes say Austen wrote only four novels because those were the books published during her lifetime. Others count Lady Susan or unfinished works, producing a different total. In standard literary references, however, “Austen’s six novels” means the six completed novels listed above, regardless of when two of them were published.