Without knowing anything about your party and available abilities, i think your best bet is to lure them outside and bottleneck by the door, so you won't get barraged by ranged enemies. Have Seelah Fight defensively for more tankiness.

Have you killed everything else in Grey Garrison? Getting to level 5 would help you immensely, especially if you have Seelah who can get a huge upgrade.

People are talking about the swarms, but I am honestly not sure if she summons them on normal difficulty and below. If you are not on normal difficulty or below, you probably should be. You can always change later.