screaming mantis

To defeat Screaming Mantis first inject yourself with the Syringe to free yourself from her control then attack her Psycho Mantis Doll, after shooting it Mantis will start to take control of Meryl, just inject her with Syringe anytime Mantis controls her. Eventually after shooting Mantis's doll enough times she will drop and you can pick it up to use it against her, you should only need to attack her with it once to beat her.

FIRST YOUUSE THE SIERINGE. THEN YOU SHOOT THE DOLLS FLOOTING BESIDE HER. THEN PICKEM UP ND USE THEM AGANIST HER

Just what the other two said but if your using the new dulshock 3 controller watch the cutscenes after you defeat er as it is different from the sixaxis one

Use syringe get mosin nagott because if you accidently kill meryl it would be game over shoot the blue/sorrow/right doll first so she wont attack you with pmc then shoot red/mantis/left doll so she wont be able to kill meryl then use synrige if you see strings over you then equip the mantis doll an use it as a weapon and it will kill her non-leathely then use the mk2 gun on the beuty and on one of the sides there is a mantis doll

You don't need to shoot the Sorrow doll [blue]. Stick yourself with the syringe (Snake will puke :P) and shoot the Mantis doll [red] and use it against her. You have to pick it up quickly before she does, or else you have to shoot it out of her hand again. You should sedate Meryl when you can. The Sorrow doll is fun though. If you get the Sorrow doll, in Shadow Moses in your next playthrough, equip it and your camera and you can hunt ghosts much easier. The Mosin Nagant idea is a really good idea.