At first, she grieves, but than she realizes that she does not need to deal with her husband anymore. We can than infer that the husband controlled her actions. She then becomes very happy because she feels like she has the power to do whatever she wants to do. Although, when it turns out that he is still alive, she dies from the shock of seeing him, symbolizing 'the joy that kills.'
I am sorry if it was not the best, but I tried.