She was portrayed by 'Susan Wooldridge in Agatha Christie's Poirot.
In the Novel
Miss Chadwick was a senior teacher at Meadowbank School for Girls, a school she had helped Honoria Bulstrode to found. When Miss Bulstrode announced that she was retiring, Miss Chadwick and Miss Vansittart would become candidates to her place's successor. However, Ms. Bulstrode annouced that Ms. Vansittart would replace Ms. Chadwick as the new headmistress, since Miss Chadwick is considered to be too old for the job. In a fit of jealousy, Ms. Chadwick killed Ms. Vansittart in the Sports Pavillion.
By the end of the novel, Ms. Chadwick was presented when Poirot made his denoument. The culprit was exposed and attempted to shoot Mrs. Upjohn, who helped to expose them, and Ms. Bulstrode attempted to shield Mrs. Upjohn. However, Ms. Chadwick had a change of heart and shielded them both from the bullet, killing her. Before she died, she confessed her crime in front of others with her dying breath.
In Agatha Christie's Poirot
In Agatha Christie's Poirot, Ms. Chadwick did not become a successful murderer since the murder and the character of Ms. Vansittart was omitted. In this adaptation, Miss Chadwick coshed Miss Rich instead, hoping that Ms. Bulstrode will nominate her (Ms. Chadwick) as her successor instead. However, Ms. Rich ultimately survives the attack.
Ms. Chadwick also survived after she shielded the headmistress from the culprit's bullet, and she confessed her crime to Ms. Bulstrode and Poirot in the hospital. Ms. Bullstrode agreed to give Ms. Chadwick a second chance to redeem herself and decided to continue her duty as the school headmistress.