Aranda

There have been many guardians throughout history from all walks of life. Aranda was just one in a long line of guardians. She served the wizards of Dalaran long ago. Years later, Medivh seemingly became the last in the line of guardians, however, his son Med'an became the new Guardian following the reformation of the Council of Tirisfal during the War against the Lich King.

Cycle of Hatred implies that Aegwynn was the first female Guardian, but it's possible she was just the first in recent memory.