There are three objects in this chapter that I think about constantly and they all mean the same thing: Xue Ning is being erased.
First, the screen. Xue Ning gave it to her eldest brother as a birthday gift for Elder Madam Jiang. It was made by Gusu Cixiu Wushuang — her, though nobody knows that yet. But when Xue Yan tries to bring it up as something positive, Xue Mingzhu immediately shuts it down: "A screen obtained from your own sister naturally wouldn't compare to one painstakingly purchased at a high price." The implication is clear — Xue Ning's gifts don't count. Her contributions don't count. Only things that are bought, performed, and presented through the right channels have value. Her talent is only valuable if it can be sold as something expensive, not given as something sincere.
Second, the oath. Xue Ning swears on her entire future — her marriage, her dignity, her life — to prove her innocence. And Xue Mingzhu, the actual guilty party, cannot bring herself to swear the same oath. The oath becomes a symbol of who has something to lose and who doesn't. Xue Ning has everything to lose and she loses it anyway. Xue Mingzhu has everything to gain and she gains it by staying silent.
Third, the Fotang. Her father orders her to the Fotang as punishment, not knowing she's already been living there. The Fotang — a Buddhist retreat house — becomes her actual home while the family lives in luxury. She gave up her courtyard, her flowers, her swing, and now even her punishment is one she's already endured. The Fotang symbolizes her complete displacement from the family she's supposed to belong to. She is literally nowhere. Not in the courtyard, not in the hearts of her family, not even in the punishment her father thinks he's giving her. She's already been there. She's always been there.