It shows that Moghedien is a step above Egwene alone, and this squares with my statement that Nynaeve not being stronger than two women out of the group of Egwene, Elayne and Aviendha Linked. This also accounts for Moghedien's reaction upon meeting Elayne and Nynaeve; Elayne was not near her full potential then, but Nynaeve was already close to Moghediens' strength - both were dangerous, but it was Nynaeve that Moghedien thought could cause more than some difficulty for Rahvin.

Rand, for example, has no chance against any of the Forsaken if they came against him in a Link - if only two Linked, he wouldn't be a match; especially since so many of the more aggressive males are close to him in strength. If Lanfear had Linked with another female, I think it would be another match not in his favor.

The closer in power you are to someone else, the less easy it is to easy Shield and dispose of them or neutralize their weaves (ie: overwhelming them). Egwene might not have a chance against Moghedien alone because Moghedien may simply be 20-25% stronger; a significant enough differentce that Moghedien could hold a Shield on Egwene without much effort while weaving a killing blow.

To put what Egwene is thinking in perspective, she has never fought to the death against a Forsaken - she doesn't really know that Moghedien is a coward, nor does she know Moghedien's combat capabilities. Moghedien is actually quite undeveloped in that area - she could have destroyed Nynaeve in a flash back in the Panarch's Palace, but instead she went for the least accurate means of defeating another channeler possible. This indicates something. Moghedien could gauge Nynaeve's strength; she already had earlier in the book. Instead of taking Nynaeve out in a surprise attack, she was beaten by her own lack of fighting capability. She didn't want to fight to the death - she wanted to capture someone in her web, and she in her turn, was captured. I think Egwene herself is quite capable of destroying Moghedien because she is not a coward, and has learned from her mistake - some threats must be killed when you have the chance, rather than captured or neutralized, because it isn't a game.