I think that your writeup is looking good, PirateJack. I'm not incredibly familiar with the threshold mechanics, but i think it's along those lines.
So i'm guessing an even semi-accurate writeup of The Siberian (who honestly has the coolest name in the wormverse) is completely impossible without some kind of 8 Refresh Strength power that basically does what Physical Immunity does for Toughness?
In case that was unclear, this is what I meant, in the form of a really rough write-up.
LEGENDARY STRENGTH [-8]
Description:Your strength is the kind of thing out of myths, because you are unrealistically strong. Things like actual gods of strength and war, extremely old giants, and elder earth elementals might have this power.
Musts:Legendary Strength replaces all other levels of Strength if taken.
Skills Affected:Might, other physical skills.
Effects:
Legendary Lifting: Whenever lifting or breaking inanimate objects, you gain +24 to your roll.
Ridiculous Strength: Roll Might at +4 whenever using that skill in conjunction with grappling. This also allows you to inflict a 5-stress hit as a supplemental action during a grapple.
Godlike Strength: Whenever using your Might to modify another skill, it always provides +4 regardless of it's comparison of your Might score to the actual skill in question.
Annihilating Blows: With attacks that depend on muscular force (Fists, Weapons, etc.), you are at +8 to damage, increasing the stress dealt by 8 on a successful hit.
Because I can't think of a single thing that a base roll of twenty-four doesn't lift or break, this might work for the "unstoppable force" aspect of her power. Her Physical Immunity is easy, but I'm not sure how to model her ability to extend it to everything she touches.