I see so much more than that happening on that stage. First of all, I think she completely nails that song. The number is a highlight of the show and a thrilling one at that. She is completely true to the circumstances Jo finds herself in at that moment in the show, and to the song itself. Secondly, I think that the emotion, the betrayal, the seething rage in that song is all the more palpable and relatable because of the completely endearing and wonderful performance she gives, starting from the first moment we meet the character of Jo in act 1. In my opinion, the fact that Jo is still there for Frankie no matter what just reinforces the feeling that the love and warmth felt for the character was well earned and well placed.