Mildred Strete is the widowed daughter of Eric Gulbrandsen and Carrie Louise Serrocold. She was married to Canon Strete, who died a year before the events of They do it with Mirrors. In Carrie Louise's complex family tree, Mildred is her only biological child. The others of Mildred's generation are self-children or adopted.
As a girl, Mildred was plain and shy. She felt that her adopted sister, Pippa, got all the attention, and that people never noticed her. When she was fifteen, her father passed away.
In 1934, when she was in her late thirties, Mildred married Canon Strete, who was ten or fifteen year older than her. They had a happy marriage, and lived a quiet life. They did not have any children. When her husband died a year before the events of the novel, Mildred moved back to Stonygates to live with her mother.
Mildred is described as a "plump middle-aged woman with grey hair". She is plain, and has "a large unexpressive face and dull eyes". Miss Marple notes that she looks "exactly like a Canon's widow, respectable and slightly dull". Inspector Curry also notes the same thing later on, and he finds it almost odd, because so few people look like what they really are.
Mildred is unhappy at Stonygates, even though it is her home. She is jealous of Gina, and feels that Gina has always been spoiled and indulged in every way. She views Gina's marriage to Walter Hudd as a tragedy, which came about when Gina was sent to America during the war, a decision which Mildred had advised her mother against.
Mildred states that the household of Stonygates is impossible. She says that her stepfather Lewis Serrocold cares only about his work, and her mother cares only about him. She is frustrated because the house and garden are not properly maintained, and not because of a shortage of money, but because no one cares.
Mildred is initially offended at having to wait the whole morning for Inspector Curry to interview her, on the day after the murder. Inspector Curry judges that it is her sense of importance that has been offended, and soothes her by telling her that it is useful to keep to the last a person whose judgment is reliable, whose testimony they can use to check what they have been told so far.
Mildred tells Inspector Curry that she thinks that Walter had killed Christian, who had probably found out a secret of Walter's. She says that she does not think Gina was in it as well, but that Walter may have killed Christian to prevent Gina from learning his secret.
Mildred later catches Alexis Restarick and Gina kissing by the lake. She is furious, and accuses Gina of trying to poison Carrie Louise.
At the end of the novel, after the deaths of Lewis Serrocold and Edgar Lawson, Mildred goes to Carrie Louise, and Carrie Louise leans on her as they walk back into the house.
Murder with Mirrors (1985)
In Murder with Mirrors (1985), Mildred is played by Dorothy Tutin. The portrayal is very close to the original movie, with a lot of tension between her and Juliet Bellever. Like in the novel, she tries to make herself useful like offering to bring Carrie Louise tea but was always being rejected because Carrie Louise says that's Juliet's job. Mildred tells Miss Marple that looking after her ill and dying husband had really made her feel wanted and useful. Miss Marple compared her to a village parallel Mary Alice Rineker who was happiest when helping someone else. Carrie Louise takes the hint and at the end of the show, Miss Bellever is dismissed and Mildred happily steps into the housekeeper/care-giver role and thanks Miss Marple for her help.
In this adaptation, Inspector Curry says that there was some suspicion about the death of Mildred's husband, as there was no attending physician when he died, and she had him cremated the next day.
BBC's Miss Marple
In the BBC 1991 adaptation of the novel which formed part of the Miss Marple series, Mildred is played by Gillian Barge. Here the portrayal is close to the original novel in that she is the widow of a vicar. However there is no Juliet Bellever here and she undertakes the role of looking after her mother.
ITV's Agatha Christie's Marple
In the ITV 2009 adaptation of the novel as part of their Agatha Christie's Marple series, Mildred is played by Sarah Smart. She is much younger than in the other portrayals. Here she is not married and is the sister of the adopted Gina. There is no tension between Mildred and Juliet Bellever. Here the tension is between Mildred and Gina. Mildred thinks that Gina has monopolised Carrie Louise's affections. Mildred plants a newspaper article about the murderess Katherine Elsworth who is Gina's real mother, probably to upset Gina and to suggest that she was the one who was trying to poison Carrie Louise. She shows some interest in Stephen Restarick although he is more interested in Gina. Mildred catches Stephen and Gina kissing, and is furious. After Stephen has been rejected by Gina, he turns to Mildred and tries to interest her in going out for a drive together but by this time she has seen through him. The show ends with Carrie Louise selling Stoneygates and closing down the reform institution and Mildred enjoying her mother's affections.