Evale and her party of elites' target was not the fort, but rather the snaking supply lines coming and going from it.
From up high, Eldrian and Ceph kept watch as Evale attacked, following the nearest supply line to find where — inside the forest and woodlands — the undead were getting all the stone.
By now, it was apparent that the undead were digging tunnels. The amount of stone flung at the border wall was enough to rebuild it twice as tall. It would be for the best if Evale could confirm this and also scout where the tunnels might lead. Even just finding the entrances would enable them to raid with better preparations.
And as the target of Evale's sortie was not to do damage but to scout, she retreated quickly after the undead moved to encircle her and those with her.