Zara Tindall has not been crowned Duchess of Sussex, and there is no official record or historic decree from King Charles bestowing this title upon her. Zara Tindall,

daughter of Princess Anne, has famously chosen a relatively private life without the use of royal titles, preferring to be known simply as Zara Tindall. She has declined the HRH title for herself and her brother, reflecting a desire for a normal life outside the intense public spotlight.
The Duchess of Sussex title remains traditionally linked with the Sussex dukedom, previously held by Meghan Markle before she was stripped of her royal titles amid ongoing family controversies. There has been no formal announcement or verified report of Zara taking over this title.
Zara’s focus continues to be on her equestrian career, family, and charitable activities rather than formal royal roles or titles. She remains popular for her grounded approach within the royal family but has not assumed the Sussex title.