I wouldn't be surprised if Isabella ended up with the exact same ability she had in Civ 5, double yields from natural wonders.
Spain's two main themes in Civ 6 are colonialism and religion, and that ability fits both of them. Natural wonders are all on different continents, so that helps the Treasure Fleets ability and the Mission improvement. They also give an agency bonus to Holy Sites, so that helps you power a strong religion.
Isabella's agenda would be that she wants to have every natural wonder on the map in her territory. She likes empires that have no natural wonders in their territory and dislikes empires who do.