In the story, Bowen uses both direct and indirect presentation/characterization to acquaint us with Mrs. Dickinson.
Direct characterization involves the author explicitly telling us what the character is like; the author may describe the character's emotional state, worldview, or perspectives on life. On the other hand, indirect characterization involves a little more engagement on the reader's part. In indirect characterization, we evaluate a character based on what the character says and does.
In the story, Bowen tells us exactly what type of woman Mrs. Dickinson is. She writes that Mrs. Dickinson is a "gallant-looking, correct woman" who is focused on preserving every outward appearance of propriety. She is also one of those women who has an "unfailing sense of what not to say" but insists on saying it anyway. Bowen tells us that "despair, perversity, or stubborn virtue must actuate" such women.
Mrs. Dickinson views her son Frederick's behavior as "abnormal" and treats it as a threat to her sanity. Bowen writes that Mrs. Dickinson uses her stoic stance as a coping mechanism and ego enhancer. Mrs. Dickinson revels in capturing the admiration of potential suitors and receives a perverted pleasure from rejecting them:
Several of them found in her straight look an involuntary appeal to themselves alone, more exciting than coquetry, deeply, nobly exciting: several wanted to marry her. But courage had given her a new intractable kind of virgin pride: she loved it too much; she could never surrender it.
Bowen also uses indirect characterization to tell us about Mrs. Dickinson. In the story, Mrs. Dickinson's words tell us that she is often indifferent to her son's emotional suffering. When Frederick cries, she tells him:
He used to be so proud of you. He and I used to look forward to what you'd be like when you were a big boy. One of the last things he ever said was: "Frederick will take care of you." You almost make me glad he's not here now.
Mrs. Dickinson's words are cruel and also manipulative. In bringing Frederick's deceased father into the conversation in such a manner, she uses the memory of a beloved parent to oppress the psyche of a young boy. Bowen's use of direct and indirect characterization gives us great insight into Mrs. Dickinson's character.
Mrs. Dickinson is the widow of an RAF pilot who died five years ago, and who is marked by the way that emotionally her life shut down with her husband's death. We are told that she only cried once after his death and refused to shed any tears in front of her son, Frederick, who now, unaccountably, has fits of crying. She is a character who insists on proper decorum in her life and to whom appearance is everything. She has massive expectations of both herself and Frederick, and as the story makes clear, these expectations are too much for Frederick's young shoulders.
She is extremely troubled by his tears and cannot understand why he should cry so much. Note how she responds to his crying fit:
She whipped out a handkerchief and dabbed at him with it under his grey felt hat, exclaiming meanwhile in tearful mortification, "You really haven’t got to be such a baby!"
She is a character who, having repressed her feelings with the death of her husband, is now so detached that her life is one big act. Tears are viewed by her as a sign of improper feminine weakness that she has done everything she can to shun. Mrs. Dickinson is therefore viewed as a product of the stiff-upper lip society of British culture, which has unfortunately distanced herself both from her son and also her own emotions, and she is shown to be worser off as a result.