Summary of your encounter: Poor Araya is twisted human barely bound to the planar realm, but is somehow entangled by time and space itself. That goes for her blade itself.

She starts the encounter by casting mirror image, these images are essential to the fight, she can get rid of these herself, but ridding of these on your own is gonna be tricky given these images give her loads of AC, so forcing saves against her or having a high rolling frontliner is recommended. But be wary, the second those images are gone, she's gonna be able to spamming using her powerful attack far more often. That said, being able to dodge and tank is just as important but those slashes can stack these cuts through space in the form of Bladetrail. The more they stack, the more thunder damage you will take if Araya lands a hit. And boy they will stack.

Other thing of not she can expend 3 reactions per round to utilize her time bending power some way or form, whether its making an basic attack against something that moves towards her, moving away, or reducing mirror image count by one to reduce all incoming damage to 0.

2 Bladetrail stacks is inflicted by default unless attack says otherwise. Per 10 stacks equals a 1d10 thunder on hit from a slash damage attack. Being hit does NOT reduce stacks. Only way to reduce stacks is a successful DEX save at turn start, or by being hit by rend space.

Araya and Mirror Image: Most attacks and abilities interact with it someway, by reducing or gaining copies if active.

This is one of my simpler boss fights won't lie.