Can't get Arya event to fire

I am playing Robb in the CoK scenario. After defeating Joffrey I plant a small army on Harrenhal with myself as the leader, hoping to get the event were Arya is found. During this time the riverlands are independent due to megawar with the Iron Isles. I wait a little over a year before defeating the iron born and still no Arya. I find the Arya character (northern girl with direwolf trait) and assign myself as her new guardian due to the riverlands reverting back to my control. After assigning myself as her guardian I still cannot get the event to fire and its been 3 years! Is there something I need to do before the event can fire? help!!