Why is her having higher AC so intimidating to you all? If Tav can have AC 18 with Scale + 1 or Half Plate, and then a shield to boost to 20, same with Lae'zel and Shadowheart, why is it acceptable for a boss bad guy to be 15 WITH shield? She should at least match the PCs in stats since she is 1 person against 4.
And yes, she has minions, but that's how boss fights work. Seriously, do you guys play video games even? This is not just a tabletop thing. At AC 15, she's one of the weakest enemies in EA so far.