Shieldbreaker is a high damage output frontline class.
She does a lot:
-High prot piercing damage
-Blight
-Destealth
-Pulling forward
-Guard break
-Buffing herself with the block status (absorbs an attacks damage, not secondary effects like bleed)
She has a unique nightmare mechanic - where after camping it's likely that an ambush-like scenario plays out where you have to fight some unique enemies while she receives a great amount of stress. If you clear all her nightmares, she stops getting them and receives buffs from camping.
There's new provisions - Aegis scales. These function like Shieldbreaker's blocking ability but can be used on any character. They carry over the hamlet if unused and are helpful against dangerous fights.
She's a fun and strong character.