I finished the dead space 2 5 minutes ago and holy shit what they showed to us man.

Your dead wife you keep seeing is not your wife but medusa!
Your character keeps saying too that she's not his wife but towards the last chapters he starts seeing her as his wife where at that point medusa takes a nice form which makes her a lot more dangerous as now your character sees her as his friend!

Her mission is using a marker=maker to burn everybody absorb them making them one with her.
After she puts you in a dollhouse machine which implants memories in your brain she tells you "to follow the light! thats where you'll find her". When you find her she's a light being and manipulates with her hands the black guy who's shooting spears at you just like athena/medusa manipulated kratos to kill himself! Pay attention to the movement of her hands in both cases!

When you kill the black guy you go to the light(which is her) hug her and rest to her arms(i told my character "stay away from her" lol) and then she told him "time to die"
He was like "what???"

And thats when he realized that she wasn't his wife but an apparition of that marker who was using him as her puppet.

Then your character tells her which were my exact thoughts too "f*ck you and your marker!" and then you go to kill her heart which is like a giant medusa head, pay attention to the snake looking things that are all around it just like on a medusa head.

She keeps telling you while you pulverize her "we need to be reborn" etc etc which is an amazing message that "reincarnation is a draconian crime"!!!

An amazing proof in that game you can get that she's not your wife but a draconian monster is in the medical clinic chapter where she talks to you through a giant screen/monitor, if you shoot at the monitor you hear a monster screaming in pain and the screen changes from your wife to a reptilian monster!
This i doubt many players would have thought to shoot at it!

Here's the ending of dead space 2