I can argue that the story turns at any of the three points! Because the runaway horse—this is the bit where Hans is going around handing out blankets and making sure people know where to go to get hot food, and then the horse shows up and Hans sends out an expedition to find Anna. And Olaf is pivotal in the concl—actually I retract the assertion that the story pivots at Olaf's song; that's more "introducing him" and just in time too since I am given to understand anyone important in the finale should be present in the first half.

But yeah, I think you're right, it's the reprise, because that's the pivot point for Elsa and Anna.