This question came up again over at Cardgamedb and I went ahead and asked FFG about it. Here was the response from Damon.
"The Northern Courser changes the claim of the challenge Arya is in. The claim replacement is incompatible with the opposing player satisfying the altered claim so the "if able" clause prevents Arya's ability from triggering." - Damon Stone
Side note - Is there anyway to get that "FFG Rulings/Answer" thread as a sticky so it can be easily found?
Edited by Slothgodfather, 23 October 2013 - 12:44 PM.