When you fight
during chapter 14, use the cranks and burn her by the lever just once. Then finish her off with the flamethrower. If done correctly she should die within a couple of seconds of using the flamethrower on her.
Note: To get the flamethrower you must pick up the broken flamethrower from the chapter 11 boss, and kill two of the flamethrower enemies to pick up two sets of flamethrower parts. Then craft it.