And Nynaeve is obviously right there with any of them. Lanfear is obviously abnormal in her raw strength, but that does automatically mean that every time a female senses another's strength they must compare to Lanfears level. Graendal notes Cyndane is stronger than she is, and comments on how rare that is, but she doesn't worry about it all that much which tells us Cyndane is not that much more powerful, and her assumed lack of skill (from Graendal's POV assuming Cyndane is a modern day Channeler). Per Sanderson Nynaeve is similar to Semirhage, who Graendal thinks was more dangerous than Demandred. That alone tells me Nynaeve's Stength would make any of the Forsaken consider her a potential threat just as Moghedien did.