So when Wraith enters Absolute Zero's Impaling Structure Hazard Space, Absolute Zero attacks her. If she has Combat Stance, does she get to retaliate on Absolute Zero? If she does, I assume her Combat Stance attack still takes things into account like range and LOS to Absolute Zero.
Yes to all of it.
What's also nice is if she has Slip the Shadows, she gets to Sprint for free, THEN make the Combat Stance strike, while completely avoiding the hazard space damage.
If the attack fails due to Slip into Shadows Wraith does not get to use Combat Stance.
Doesn't it say when the attack resolves? Slip the Shadow specifically says any attack that fails because she moved resolves as a miss.
I'd always been under that impression as well, so the two together allow her to sprint (possibly avoiding the attack) and counterstrike. Normally, only useful against melee attacks, since combat stance resolves second, so the counterstrike wouldn't have LOS if the shift moved out of LOS of the original attack, but also works against area attacks and external hazard generators, since the attacker and the source of the attack are not the same, so she can sometimes maintain LOS to the former while obstructing it from the latter.