Malys and psychic powers

Am i right in thinking Malys would not be instant killed by a force weapon?

Pg. 50 of the BRB seems to pretty clearly define the insta kill effect as a psychic power - so I would say, yes, she and her squad are immune to it.

Not that it would matter much but would psy-ammo not work against her? Sure, it would still insta-gib her but would the shots be -1 strength?

No, it will work, because it's no psychic power, just ordinary wargear.
It says it uses psychic energy, in it's fluff, but that's not enough.

I'd agree with that.

How about the Nemesis Force Weapons of the Grey Knights? I think they don't test after making the wound like regular Force Weapons (which would be blocked by Malys), but rather test before swinging and if passed the entire squad causes insta-gib. That is a USR and therefore not blocked by Malys, correct?

Again no, they use Force weapons, as described in the BRB. They just roll once after the first wound, instead for everyone separate.

Oh, so a unit of Grotesques with Lady Malys would indeed be a nice thing to have against GK, yes? Awesome!

I believe there still a power weapon therefore still no, feel no pain.

Of course, the question was about their ability to insta-kill things that suffer one wound. A power weapon is still a power weapon regardless of immunity to psychic powers.

However, you have to take a Psychic test to use a Force Weapon and you cannot use it if you have already used a Psychic shooting attack previously in the turn (unless you can use more than one power a turn).

From that I'd say it DOES count as a Psychic power.

That should be you can't use your FW if you have used ANY psychic power previously unless you have a rule letting you use 2 or more per turn(player turn remember!)

That said, it is indeed a psychic power and the instant death component is negated by Malys

Urien Rakarth wrote:

However, you have to take a Psychic test to use a Force Weapon and you cannot use it if you have already used a Psychic shooting attack previously in the turn (unless you can use more than one power a turn).

From that I'd say it DOES count as a Psychic power.

Yes, as I said, you're immune to the insta death effect.
A force Weapon's power weapon component is part of it being a weapon however and requires no power to activate - thus it's still a power weapon and that still works on you. They just can't instaglib your grots.