"I mean to save my Mother."
Aeliš of the Moonleaf was born on the side of the road between Dryadis and Stin Cepel. She got her name because she was born by a plant which reacted to the light of the moon. Her twin sister, Jeyne, came a while later, born at the break of dawn, and was called Jeyne of the Dawnbreak.
Aeliš grew up happy with her sister. They were nearly inseparable for their entire lives. When Jeyne pledged her life to Melora's service, Aeliš volunteered as well. So, when Melora joined the Consortium in the Astral Civil War and called her followers to the Astral Sea, Aeliš went, though not enthusiastically.
Though her sister downplayed the dangers, instead focusing on the excitement, Aeliš could not shake the bad feeling in the pit of her stomach. Her worst fears were realized when her sister was chosen for a top-secret mission and she was not. Jeyne never returned from the mission, killed in action by Coalition forces, but Aeliš blamed the Consortium.
Aeliš went on a scouting mission to the Isle of Beasts to hunt down two of her friends who had gone missing. While there, she ran into Quen, who was tracking down a lead about a Vis'tani clan. The two, obviously on different sides of the war, created an uneasy truce, recognizing they had a better chance in the jungle together. In speaking with Quen, Aeliš came up with only more questions about why Melora had joined the Consortium.
Aeliš found her friends - they had been killed by the Vis'tani clan, defending their territory. Meanwhile, her "allies" had begun to burn the jungle down. Quen offered her a chance to come with them through a portal back to Kilat, and after a split-second of indecision, Aeliš agreed.
While recovering from a leg wound, Aeliš came to the conclusion that Melora had been misguided. She decided to make it her mission to save her Mother, her goddess. So, she defected to the Coalition. She shared intel about a certain enemy War Camp, as well as other information, with the condition that she be allowed to return to the Isle of Leaves.
And return she did. Aeliš made her way to Melora's throne and forced Mother Nature to face all the destruction wrought in her name, Melora turned coat that day, sending forces to the War Camp Assault which would arguably prove to be the deciding factor in the battle.