User blog comment:Xilinoc/Ch. 568. Hear. Fear. Here 2/@comment-2120712-20140214182206/@comment-5693502-20140214185938

Even with her power up, I strongly doubt there were any (remaining) Sternritter that Rukia could've defeated by herself. Simple reason being she doesn't possess bankai. Again, even with her completed "absolute zero" temperature ability, her chances of beating one of the remaining Sternritter is really quite low.

Rukia isn't and has never been Captain-class and also she hasn't achieved bankai. Correct me if I'm wrong, but (excluding Zaraki Kenpachi for obvious reasons) I can't remember any Shinigami that had clearly beaten their opponent having only possessed a shikai.