@Prince of Seraphs Not accompany. Receive. At her palace in winter. Someone has to go with through her lands, or how can they report that it reached her properly? I'm sure the fey might say that it never reached its destination -- and certainly that would be true if they had it deliberately diverted.
If it were a one time delivery that might be cause for concern but this is an established exchange that had been going for a very long time. Were Arys to claim that the food never made it and demand her goods back it would put unnecessary strain on future negotiations and since Winter has cut itself off from Summer that would leave it with only Fall to supply anything that Winter cannot generate itself. Politically speaking it would be a bad move for too little reward.
The more logical thing would be to have some proof that the exchange on the border took place. Say the exchange of a token or some such. Once this exchange is finished and there is proof that it took place it is the responsibility of the ruler of the Court the goods are passing through to make sure the goods arrive safe. That way if bandits attack the convoy after the exchange has been made Winter cannot blame Spring for the loss of goods. Likewise if Spring's goods are stolen they cannot blame Winter. It takes some of the political tension away and limits the rulers from pulling something over on the other. If Sini were to accompany the convoy into Winter lands and it was attacked or Arys arranged for it to be robbed the Winter Queen could blame the loss on Sini's incompetence and demand the food be replaced or her own goods returned.
