Like most resources in Hyrule Warriors: Age of Calamity, Silent Princess is a scarce and much-needed one to level up characters like Zelda and unlock various things on the map. What makes it different from every other flower in the game, though, is that it doesn’t have one single area where can be collected on the battlefield. This resource is incredibly hard to come by because it can only be unlocked and gathered through certain conditions.
Early on, Silent Princess can only be gathered through mission rewards. While searching through the map early might not show anything, after you reach Chapter 3, extra challenges and missions should appear that offer Silent Princess as a reward.
More of these subquests will open up over time as you complete the main story, giving you an ample supply of Silent Princess to help you complete all the objectives scattered around Hyrule. So if you are looking for them in the early game, just wait. They will turn up eventually.