Final answer:
Anne is eagerly anticipating the fancy-dress ball at the Stenborgs', showing her excitement for both the event and the opportunity to surprise her husband with her attire.
Step-by-step explanation:
The upcoming event that Anne is looking forward to with such eager anticipation is the fancy-dress ball at the Stenborgs' place. This is evident from the excerpt where Nora expresses her excitement about attending and dressing up for this event. We can infer that this ball is of great significance to her, given the level of enthusiasm with which she is awaiting it, and perhaps also looking to surprise her husband, Helmer, with her attire.