It just occurred to me that Arianne might be planning to give fAegon the Valyrian steel Crown of Aegon I. Daeron I was likely wearing it when he was killed. Doran could very well still have it. What do you think? Caveat: I’m only up to the Westerlands chapter of WOIAF.

The Crown of Aegon I was indeed lost in Dorne: 

“"Such was his desire to split from the past that he had a new crown made–a warlike crown with black iron points in a band of red gold, since Aegon the conqueror’s crown had been lost after Daeron I’s death in Dorne.“ (From the Maekar I section)