Anthea is "thin with grey hair that had once been fair hanging untidily on her shoulders and a faintly wraithlike appearance". Miss Marple thinks that she could successfully be cast as a mature Ophelia.
Anthea has one eyelid which twitches from time to time, and large grey eyes. She has an odd way of glancing right and left, and then suddenly behind her over her shoulder, as if she feels that someone is watching her all the time.
Anthea is described as being vague and scatty, and her sister Lavinia mentions that she sometimes wanders off, and does not seem to know where she is.
When Miss Marple first comes to The Old Manor House, Anthea takes her on a tour of the garden, and shows her the remains of their old greenhouse, which had fallen down as they did not have the money to repair it. The remains of the greenhouse are covered by a flowering creeper, Polygonum Baldschuanicum.
According to Lavinia, Anthea remembers how the garden used to be, and worries about it, wanting to spend money to put it right again. Anthea had once tried to engage an expensive firm of landscape gardeners to renovate the garden and build up the greenhouse. Clotilde had found the estimate for this work on Anthea's desk, and had been extremely angry.
Miss Marple later sees Anthea going to the post office with a big parcel. Enquiries at the post office reveal that the parcel was sent to The East Ham Women and Children's Woolen Clothing Appeal.
When Miss Marple brings up the name "Verity" in front of the three sisters, Anthea's reaction is "quick, excited, almost pleasurable". She asks if Miss Marple is referring to Verity Hunt, and tells her that Verity died in an awful way, and the body was found in a ditch. Clotilde tries to stop her from talking, but Miss Marple observes that there is "never any holding Anthea", once she begins talking.
Miss Marple also observes the "somewhat slapdash manner" in which Anthea helps her pack her belongings, and forms the opinion that Anthea cannot fold anything properly.
Miss Marple is told that Anthea has always been rather unbalanced, and was rather delicate as a girl. Anthea is said to have fits of hysteria, to have queer ideas, and say queer things. She is also said to have been jealous of Verity, and to look at her as though she hated her. When she was quite young, she was said to have wrung the neck of the family's parrot.
Miss Marple later explains that Anthea knew who had killed Verity, and was afraid of what the murderer might do. The murderer had told Miss Marple that Anthea was mentally unbalanced, and that she had been jealous of Verity. Miss Marple thought that if the murderer had not been found out, in the future something might have happened to Anthea, such as an arranged suicide because of a guilty conscience.