Answer:
The evidence is the phrase: "You don't know what that letter can bring upon us."
Step-by-step explanation:
According to the context of the question above, we can see that it refers to the play "A Doll's House" which shows a marriage that was completely destroyed due to the revelation of a great secret. This is the marriage between Nora and Torvald and the secret involves a third person, Kronstad.
Nora is very afraid of how her husband will react if he discovers the secret and we can see this fear through the phrase "You don't know what that letter can bring upon us" where she shows how apprehensive about the consequences this letter will provoke to marriage.