No, Rococo was around the 1730s (mainly in France) and died out around the 1780s. Jane Austen was writing at the end of the 1700s (18th century) and beginning of the 1800s (19th century). We associate her with the British Regency Period, which was from 1811-1820. She wrote her most famous books in that time; the Prince Regent himself was a fan!
In the films and TV series we see of her work the fashions are most definitely Regency, with the graceful Grecian-like dresses.

