She is tall for a Cairhienin, although of average height (about 5'4 tall), and elegant and graceful. She is pale and has large dark eyes. She somehow seems beautiful without being at all pretty. She owns a dress of blue slashed silk, with red and gold embroidered on the bodice. 
Strength and Abilities
This is not confirmed by "The Wheel of Time Companion" where her level of strength is described only as 24(12), a very low level for a Sitter, almost the level of an average Aes Sedai. This is probably a mistake because eleven levels below the strongest Sitters would mean that Lyrelle is a too weak Sitter compared to them.
Lyrelle's true level of strength can be guessed by the time she spent as novice and Accepted which was in total only 10 years, roughly the same as sisters that are between levels 16(4) and 18(6), in fact the time spent in training usually reflects the strength of an Aes Sedai (for instance Verin and Merana stayed in training 11 years, and Alanna, Teslyn and Joline for 12 years, all of them are at level 17(5).
Lyrelle was born in the year 833 NE, so she is 167 years old. She went to the Tower in 849 NE. After spending six years as novice and four years as Accepted she was raised to the shawl in the year 861 NE. She was elected Sitter recently in the year 995 NE.
Some say she was a dancer before coming to the White Tower as a novice. In fact she still moves with extreme grace.
War against Elaida's White Tower
Black Tower alliance
After small prodding from Lelaine, Lyrelle voted yes in the rebel Hall of the Tower for an alliance with the Black Tower,  and during Lelaine's emergency meeting of the Hall, she stood to accept the offer from the Dragon Reborn of bonding forty-seven Asha'man.
After this decision Lyrelle was among the sisters sent to bond the Asha'man, but at the Black Tower, she and her embassy were denied entrance for the moment, and so they camped outside its boundaries, waiting. Seaine Herimon was sent from the White Tower to warn them of the Black sisters among their ranks, though it was said that any Blacks among them had already escaped.
Later, once the Black Tower had been cleansed, Lyrelle was in charge of the delegation waiting to access to the Black Tower; Lyrelle, Myrelle Berengari, Aledrin, Seaine, Faolain and Theodrin, among others hastily called from the Last Battle, greeted the leaders of the liberated Asha'man, Androl Genhald and his bonded Aes Sedai, Pevara Tazanovni, and were given their promised forty-seven Asha'man
Lyrelle, showing her thought for the first time, was frustrated that she lost opportunities to prove her leadership during the reunification of the Tower. She initially thought of how to use the powerful Asha'man to gain influence and wriggle out from under Lelaine's thumb; she even considered using the Warder bond to compel them. Later she was annoyed at finding that the only Asha'men remaining in the Black Tower were those who volunteered to become Warders, spoiling her plan of bonding one and making him point out which ones were the strongest. This fulfilled the terms of Rand's bargain - that no Asha'man asked to be bonded may refuse. The ones who did not want to be bonded simply left.