In truth, Aviendha and Egwene together would not exceed Lanfear's strength. That was Moiraine's desperate hope, but we see that just one book previously, Egwene plus Elayne - who equals Aviendha in strength - could not even come close to matching an undeveloped Rand, who is not yet equal to Lanfear in strength.

Therefore the reality is that at the time of FoH Egwene and Aviendha combined would have no hope of matching Lanfear's raw strength.