She is a short and slender Cairhienin with glossy black hair and large liquid dark eyes. She is pale skinned and elegant.
Merilille is not particularly strong in the One Power. Her level of strength is described by "The Wheel of Time Companion" as 22(10) which is a middle/high level in Aes Sedai hierarchy. This level of strength can be just enough to open alone a suitable gateway to Travel.
She allies herself with the Salidar Aes Sedai and is sent as their ambassador to the Ebou Dari court. In particular Merilille was the leader of the embassy and while inside the Tarasin Palace in Ebou Dar, she vigorously opposes the White Tower delegation when they suggest that Matrim Cauthon should be returned to the White Tower.
She later dresses down Elayne Trakand for almost revealing to the Kin that the White Tower knows of their existence. Elayne in turn sets Merilille in her place and takes charge of the embassy using her higher standing in the One Power as reason.
The Windfinders have claimed Merilille as their teacher in payment for their assistance with the Bowl of the Winds. She is kept constantly busy with teaching them and is sometimes used as a test subject for their lessons. She is regarded as lower than even an apprentice. She has become increasingly withdrawn and subservient.
Some time after she is sent by Elayne to meet with the Borderlander rulers that have camped down in Braem Wood with their huge armies. She reports back to the Daughter Heir about the state of the camp and is sent back again to prepare the meeting between Elayne herself and the rulers.
Merilille fled the Royal Palace in Caemlyn probably because of the unfair treatment suffered from the Sea Folk and surely fearing to being sent to the Athan'n Mier ships for one year, following the bargain obtained by Nynaeve and Elayne; one of the Windfinder apprentices, Talaan din Gelyn, fled with her.
During the Last Battle Talaan was fighting in Thakan'dar, so probably also Merilille was there.