Yeah I think we made that puzzle too hard (:
Hint: The answer is NOT found explicitly in any text message nor calendar event. You'll have to figure it out through context. I'd recommend reading the Wednesday calendar reminder that Caspian left himself first. From his text chain with Jade afterwards, it should be clear she did _some_ favor for him... but what? And when? If you can piece that together, you'll be very close to the answer...
Hint 2: If you're still stuck: try the conversation with Maddy. What is Caspian upset about? Jade's favor is related to that.