In perusing tGS I came across the chapter where Daigian is teach Nynaeve the 100 weaves, and something struck me. Nynaeve has suddenly had a couple of revelations... She can now sense the strength of other women AND she is no longer insecure about her strength. As you may recall from earlier books she was quite incapable of measuring Alivia's strength, and she was nervous around her because all she knew from others was that Alivia was stronger than her and that in Nynaeve's head she would have to stop Alivia from killing Rand... suddenly in tGS, Nynaeve has this to say

The Plan For Arad Doman

"She herself was so strong in the Power -- one of the strongest alive -- that she often took little thought for her ability. It was much as a very tall man rarely paid attention to other people's heights; everyone else was shorter than he, and so their different heights didn't matter much."

I bring this up because I'm starting to believe that Nynaeve has had something of an epiphany since encountering Semirhage, and realizing that she herself is in fact stronger than yet another Forsaken. She already knew she matched Moghedien months prior, now she's been face to face with another woman who is supposed to be so far above them in strength and she at least matches her!

IMO if Semirhage was indeed stronger than Nynaeve we'd have heard some worry about it. Yes I know this is thin, but from Nynaeve's prior whining about Alivia and even her complaints about Talaan being her equal, I'm certain she would have had some additional commentary if Semirhage had in fact been the stronger of them.