Mordrellen is Queen of Andor. Her death, after the disappearance of her daughter Tigraine, leads to the Succession that eventually puts Morgase on the Lion Throne. (TFoH,Ch19)
Other References
TFoH,Ch19 - Morgase married Taringail for political reasons only. He was the husband of Tigraine, daughter of the previous Queen Mordrellen.
CoT,Ch11 – The Andoran succession is normally straightforward. Mantear only lost the throne to Trakand because Tigraine was missing when Mordrellen died.
Books 