This part of the game throws a lot of enemies at you at the same time. If you have the Lightning Shield though, it gets pretty easy.
Leanna is alive! Who saw that coming huh?
Anyway, in the part where I use the Sanctuary scroll there are around 5 or 6 necromancers and 2 black guards, so it is recommended to use the scroll at that part.
Also, this is the first part that I actually exploit the use of Stoneskin Potions. They'll make you invincible for the fight against the Giant spider. The battle can be done without using the stoneskin potions but it would require the unnecessary use of health potions.
And take note that after you rescue Leanna she starts to act really weird and it may possible that she'll stop following you. If that's the case just go on without her, you'll still find her back in Stonehelm.
Just leave the necromancer lairs and go back to Stonehelm. Remember to always leave Leanna behind, otherwise she could get killed in the midst of battle.