Anna's got three weeks of exams (or thereabouts) and then the weekend off for Thanksgiving before going back until Christmas.
It makes her life all very hectic. Several times, Elsa has to shake her awake from where she's bent over the coffee table, a terrible soap on TV as pure background noise to her studying, dozing on her textbooks.
She's working too hard, but it means the awkwardness of Halloween disappears amongst the stress and exhaustion.
Anna simply doesn't have time to think about Elsa and how she feels towards her. Or, what those feelings mean.