a good way to complete this mission is to build a tower that can hold a siege weapon near the outer gatehouse.
place a MANGONEL in there
fill the tower with as many crossbowmen as possible
on the overlooking wall (the one with the two towers, place all your archers there
order the mangonet to fire as close to the river as possible.
when the Wolf attacks the crossbowmen should have a devestating effect on all troops. the archers should be of some help and the mangonel should take out a few men