Even the song of the Hårga is told from the first person plural, the “we” of the dancers. They are all invested in the ritual. If one of them wins, they all win. When Dani is the last dancer standing, her new family celebrates with her. They are there for her when she grieves her boyfriend, too.
I love the ending of Midsommar because I feel like Dani really comes into her own; it’s the first time she’s had agency or presented with a choice, in my opinion, throughout the film. As you know, the May Queen is not sacrificed as many of us likely intuited: instead, she’s lifted on a platform and carried to her flower throne. She follows the sounds of another ritual though her now-sisters advise her against it. They go with her anyway. She sees her boyfriend having sex with someone else. She hyperventilates. Her new family is there, with her, breathing with her and comforting her in an empathy so physical it’s uncomfortable to the viewer.
Then, Dani discovers that the May Queen gets to choose the final sacrifice, from between Christian and a member of her new family. She chooses her boyfriend.
Here’s the thing, though: I don’t think she chooses him because he’s “cheating” on her. That ritual, to me, is absolutely a rape, for one. That Christian has a terrible time at the festival is a gross understatement, but the thing to remember is that Christian was shitty way before they came to Sweden, and Dani, like so many women complacent in their relationships, women clinging to a dysfunctional relationship because the rest of their world has crashed, women set adrift from the world, clings to him like a life raft, even though he will not keep her afloat.
During the dance, Dani finds support, love, joy, and that is (in my interpretation of the competition) why she wins. It’s not until she finds that community in Hårga, specifically in the dance with the other women, that she can release the last tether to her unhappiness and set him on fire.