During the night, Edward will leave the house and get into a battle with a Water Hag.
Water Hag:
It�s easy. Anna will appear during the battle giving words of encouragement, so just attack and the Water Hag will fall.
In the morning, go to the weapon shop and buy 50 Brass arrows to equip on Rosa. There�s nothing else to do, so go back to where the Antlion�s den was, but continue past it to Mount Hobs.