Based on what i had read on the last few days i can confidently say that the situation that both Nora and Krogstad are in is very vital. If the wrong person were to know the confidential information that Nora and krogstad had both known the relationships of all protagonists would change, especially between Nora and Torvald. As stated on page 190  "whatever happens , when it comes to the point you can be quite sure that i shall have the necessary courage and strength. you'll see that i'm man enough to take it all on by myself"(Ibsen 200) Helmer is proving that he is ready to face such information without the consent of everyone. how ever Nora still does not want him to know what the contents of the letter are in any circumstances. For any one to know this information this would bring a huge INTOLERABLE  reputation to not only Nora for doing the work but for Helmer who is supposed to be doing the work.
                   Towards the end it gets a bit weird as Nora gets a bit desperate with Helmer not knowing the content of the letter. Despite being very anxious and worried she played a very JAUNTILY like facade. She goes to an extent as to where she does very raunchy things like showing her legs and what not which is the equivalent to "flashing" in today's time which most of the society would REPROACH if done. as stated on page 193-194 "Silk stockings- Flesh coloured  aren't they lovely? the lights bad in here now but  tomorrow... no no no you must only look at the feet oh well you may see the rest too..... There is no one else id trust more than you. i know your my best friend most faithful friend so i'll tell you... well, dr rank - its something you must help me to stave  off. you know how much-  how incredibly deeply- torvald loves me. he wouldn't hesitate for a moment to give his life for me." (Ibsen 200) with this really odd like way to persuade a man in to giving her what she wants she fails in a weird way as Rank admits his feelings to her which ruin the moment. She even stated that she didn't like how it ruined it.
                     in my honest opinion i feel that the second act was probably the best out of all of them as all the tension is building up ,and watching the characters reveal their true colors as they go is priceless. i honestly can not wait for the next part :)