I think Sable surpassing or reaching her level will and must happen in the middle part of the story. Then again she's one of the important characters.

Sable's hurdles goes like this.

Sable = Aiden(equal)--Gwen(2 gaps)-----Sairis--Nathan-------------------------------Marduk.
Also, Gwen is not taking out Sable and Aiden at the same time.

That being said, really need to get Gwen fight more and fleshed out more, no puns intended, she shown too much flesh xD