The Elves of Irollan before the reign of king Arniel, elected their kings. When Arniel came to power he declared that his bloodline will be kings from hence forth. Tuidhana did not agree with this decree and so did many others, but she was the only one that took action. She then separated from Irollan in the year 528 YSD in the caves below the earth and became the first queen of Dark Elves. When the Holy Falcon Empire attacked her land starting the war of The Bitter Ashes in the year 540 YSD. The war took place on her land, which was on the border between the two nations. She pleaded for help from the Elven king, her messengers were turned away every time, and with Arniel stating "She stands alone, she fights alone".
Arniel entered the war a while later, and the battlefield was on Tuidhana's kingdom. Neither side took care of the damage that was done on her kingdom nor her people. Tuidhana gets into contact with one of the few remaining faceless, who state if she and her followers worship the Dragon of Darkness, Malassa, she will get the power to protect her people. The pact is made, her and her followers are turned into dark elves. With their new allies she is able to drive off the elves and the Holy Falcon Empire from her land. An uneasy alliance is made between the elves and the dark elves. However, her death split the Dark Elves into smaller clans.
In Might & Magic X: Legacy, the party can find the book about Tuidhana. There's story of her unhappy family, siblings and parents, and her terrible deals. Though this is not clear it's true or not.