Anna forgets to be sad when she and Elsa talk. They converse about the most mundane things, and it's... really pleasant. They talk about school – Anna's studies, and Elsa's class.
Being told that a mother-to-be teaches six-year-olds is... well. Anna didn't expect it, but it fits Elsa perfectly. Elsa and children go together. They match.
But, it's also the holidays, and it's obvious that Elsa is feeling... restricted. Alone, possibly. After all, she is spending the day with Anna.
But Anna says nothing. She doesn't want to ruin this.