Deborah Harper

Chapter: L2 · Cemetery & Cathedral
Chapter: A2 · The Forest Cemetery, the Simmons Crypts, Deborah and the Underground Lab
Where: 2-6 Primitive Altar (Leon) / 2-2 Altar Corridor (Ada): a two-level chamber, the descent through the mine, the mine cart and the final platform. **Story Intersection** between Leon Chapter 2 and Ada Chapter 2.

Weak point

The glowing orange and yellow glands on the tentacles on her back; her human body is practically invulnerable

Helena's sister, turned into a chrysalid by the C-Virus. Damage goes in through the glands on her tentacles, which shatter after a few handgun shots; body shots do little. Four attacks: chest-pierce strike (spins down from above and impales you: wiggle out and counter), a long horizontal claw swing at ground level, a dash attack with her claws out and a 360 spin (back off as she jumps). When she screams, she leaps at you: dodge. It's a phased fight: chamber, descent, mine cart and finish. In Leon's campaign Ada fights alongside you; in Ada's, Leon and Helena are AI when you play offline.

Reward

In Leon Chapter 2 it ends the chapter (achievement Buried Secrets). She drops nothing: your ammo comes from the zombies. A medal in both Leon Chapter 2 and Ada Chapter 2: Killed 5 zombies while in the minecart; in Leon Chapter 2, also Relieved Deborah of her suffering.

Health per phase from a single source (trainer reads, difficulty not stated): 5,000 on mutating, 30,000 in the chamber, 8,000 in the mine tunnel, 5,000 on the cart and 3,000 at the finish. For scale, that 30,000 is about 25 Lightning Hawk shots on Normal with no skills.

Step by step

Shoot her a few times until a short scene plays: the real fight starts there.
Aim for the glands on the tentacles. When she poses on the upper level with the appendages out, it's free damage (dual Wing Shooters as Helena, the Ammo Box 50 as Ada).
There are 2 explosive barrels: only shoot one when she's right next to it.
With enough damage she falls on her back with a tentacle out: get close, melee and follow the on-screen buttons to tear off a claw. 3 tentacles destroyed triggers the scene.
If she straddles Helena, help her: a human Helena who fails that QTE takes heavy damage or dies.
Zombies spawn now and then: they're weak and drop ammo (shoot their lanterns).
Split before the cart: in Leon Chapter 2, Helena and Ada go down first and cover Leon, who descends through the mine past zombies and turns the crank; in Ada Chapter 2, Ada and Helena drop into the cart and Leon works the switches.
Mine cart: lie on your back (aim and hop backwards). Prone, you avoid the 4 beams and almost all her attacks. Ada must hold a weapon other than the crossbow or she only backflips. Shotgun her glowing parts from the floor.
Shoot the TNT drum at the roadblock on the track before you reach it, or it's game over. The other 2 barrels on the track only hurt you.
Finish: after the crash, grab the ammo and shoot the glowing tentacle tip aimed at Helena before the platform gives way. Time is short: the sniper rifle is fastest. Too slow and it's game over.