Luke reacted as strongly as he did because he was told by Vader himself at the end of an exhausting duel, when for all he knew Luke still might have lost his friends (all he had left in the galaxy after his aunt and uncle were murdered), and after the emotion of leaving his training. Had he been told by Leia during a quiet break in the action I bet he would have been much calmer as well.
Its something that Leia would need to process for a while and she would have some confused emotions I am sure.