Cassandra Dimitrescu

Chapter: 4 · Castle Dimitrescu
Where: The Armory (2F), a small room full of furniture that you reach through the Hall of Pleasure fireplace.

Weak point

The cold behind a cracked wall. Same factors as Bela: ×2.0 from handguns, rifles and magnums; ×1.6 from shotguns.

Before the fight she shows up in the Private Corridor, the Main Hall and by the Dining Room doors (after the Courtyard Key): she phases through doors as a swarm and gives up if you get far enough away. Don't shoot her there.

Taking the Mask of Pleasure locks the door; crouch through the fireplace and go up the stairs into the Armory and she appears as soon as you enter. The key is blowing open the corner wall with a Pipe Bomb to let the cold in.

Reward

Crystal Torso (5,000 Lei). Afterwards take the Mounted Animal Skull from above the west fireplace to get out of the Hall of Pleasure.

3,400 HP. Rough estimate at Standard's starting rank: about 34 un-upgraded LEMI shots or 8 M1897 blasts.

Village of Shadows: same plan; an infinite-ammo magnum (New Game+) ends it in seconds.
Knives Out: the Pipe Bomb on the wall is required and does not count as a gun kill.

Step by step

If you have no Pipe Bomb, take the 2 Pipe Bombs from the Armory's north-west table.
In the far corner, push the cabinet (yellow tape) away from the wall: behind it is a crack with sunlight.
Throw a Pipe Bomb at the crack. Cold air pours in. The blast does her no damage.
Keep your distance (up close she claws and her flies block your view) and use the furniture to slow her down.
Shoot her in the head until she shatters. Ammo in the room: Handgun Ammo ×15 (Standard only) and Shotgun Ammo ×2 on the south-east barrels.