@ligma in the hayday of monarchies they would take members of other kingdoms high ranking nobles or royal families as political hostages. This was to display that kingdoms subservience to the hostage takers kingdom. If the hostages kingdom betrayed or failed to meet the demands they would be publicly executed, their body put up for public display, and a war would possibly occur. So the purpose of taking her was to exploit Berry for whatever he wanted. Trade, soldiers for a war, or tribute.