Looking for title on fantasy book most likely from the 90's

I will try to include as much as I can remember.

I believe the book series was a trilogy Main heroine was a female white haired Mage/sorceress whose birth was orchestrated by magical beings in order to combat evil mages/sorcerers. Her companion was death who I remember she fell in love with and she dies/ascends at the end if the trilogy after defeating evil. A very specific detail that I do remember is one of the evil Mage/sorcerer building a tower and using human remains as mirror.