Actress Nicola Coughlan, who plays Penelope Featherington but was revealed as the allusive figure behind the Lady Whistledown character in season one, also features in the teaser clip.

Source: https://jerseyeveningpost.com/morenews/entertainment/2023/12/12/netflix-reveals-bridgerton-season-three-will-premiere-in-two-parts/

Lady Whistledown also released a statement of her own regarding season 3 on May 16: “It is only fair that in this author’s third year chronicling the marriage mart, Mayfair’s social season should find its focus on a third son… as well as a third daughter.

Source: https://hollywoodlife.com/feature/bridgerton-season-3-4685217/

Not only does need to keep Whistledown for plot purposes, it also needs to maintain Penelope's passion for writing.

Source: https://screenrant.com/bridgerton-lady-whistledown-penelope-season-3-must-keep/