Serena saw the deeds and was reminded of their silly conversations in the past. At that time, though she was the daughter of one of the richest dukes in the kingdom, she still wanted money for security. Just in case she and Charlton were to run away. Yet now, looking at the deeds, well, there's a part of her that's touched because Charlton remembered, but the charm of the monetary value it held felt irrelevant.
Maybe it was because she already became the crown princess. Don't get her wrong, even then, money was valuable, but when one is in that position, money sometimes feel like nothing but a number.