She goes to Thalassar. Sometimes you can see where NPC's go if you export your NPC memories, and then look at their list of things they do, it'll see "So and so exited Silverpine" And Oriana goes to capitol weekly for some reason. I never asked her about it, and it'd be hard to know if the AI will drum up something out of thin air for the sake of roleplay or if there is actually something in her memories put their by the developer for the AI to referance.
That could be something new. In the past, when checking Oriana's memories I've never seen her go to the Capital, it's always been Celandine who goes there. Oriana would always "meditate in the mountains" when it's her turn to be away from Silverpine for the day. She usually goes straight south from her house and doesn't use the road to leave the area. Which was always weird if she was going towards the mountains, why go south and not west?
Anyway, you might be right, but I know she doesn't like to go to loud/noisy places, or at least that's how the AI spins it when I asked if she goes there or why I never see her in Gareth's tavern.
Oh actually, you could be right, I might have mixed the two sisters up, I just remember one of them would disappear sometimes and the AI generally hallucinates if you ask them where something is so I just checked the memories and they were at the capital. It probably was Celandine and I just mis-remembered it as Oriana.