Oh, and I suppose not being able to fly also means gravity is exempt from Siberian’s ability to deny forces from applying to herself. Though turning off gravity would be more like super-jumping than flying, that would still apply to the Triumvirate fights as a way to get high enough to hit them.
And hey, even besides the usual flexibility of powers (like how glass powers may or may not affect sand), that can be explained by the fact that not all models interpret gravity as a force. General relativity, for example, famously interprets it as curvatures in spacetime instead.
By the way, I do think that with the forces she can deny, it’s not an on/off “forces apply to me” vs. “forces don’t apply to me”, but rather a flexible thing where she can pick and choose which forces do still apply. Otherwise, she wouldn’t be able to walk/run while her power was active, as the reaction to her pushing against the ground wouldn’t push her forward.