In the beginning of scene ten, Margaret and Harriet are trying their best to comfort Sylvia about Gellburg’s critical condition, saying she mustn’t blame herself, as it could happen to anyone. Sylvia finally begins to talk about the beginning of her relationship with Gellburg, when they first got married and Sylvia comes to think that she is stronger than Gellburg, however based on the period in which they live she claims to swallow the truth and “make believe you’re weaker.” Harriet doesn’t really seem to react to anything being said, and when her sister finally breaks down and begins crying, she says something about a pot roast and leaves. I think this shows Harriet’s inability to cope with a stressful situation and possibly reflects her immaturity.
Margaret and Sylvia are then left alone. I think this is why Sylvia choses to open up to her rather than Harriet. I believe Sylvia has tried to do so in the past however Harriet seems to always reply with an almost rehearsed response, as if she’s automated to respond in a certain way. Margaret instantly starts bestowing wisdom on Sylvia. I think Margaret earns Sylvia’s respect instantly. Perhaps she thinks that Margaret can empathise with her, or gets the impression that they both feel the same.
Margaret seems to have moments all through the play where she reflects Sylvia’s dissatisfaction with life, and I think Sylvia might be able to see this and that is why she is instantly open with her.
Another thing may be that Harriet is simply not on the same intellectual level that Margaret is. It may be that Sylvia feels that Margaret may be on par intellectually with her, rather than Harriet who we see throughout the play to be mentally inferior to Sylvia.
I also think that it could be that Sylvia is using Margaret as one would use a confession booth, to a degree. She knows Harriet, very well, and knows that anything she says to her will be remembered and probably brought back up in future,