There were many stories regarding the origins of the Maiden of Virtue, but the official website never confirmed any of it.
Some people thought that she came here by herself for the sake of protecting this world alongside the guardians. Then, she discovered that there was something wrong with Medivh, so she stayed and tried to use the power of love to change him.
Some people also thought that the Maiden of Virtue was created by Sargeras. She definitely wasn't to Medivh's liking.
Karazhan was an odd place. There was corruption, but there was also innocence. There was immorality and there was holiness. There was also loyalty and yet also betrayal. No matter what, Maiden of the Virtue was a Boss. Furthermore, she was also more powerful than Moroes.
The first few times of battling her were bound to be difficult. This was because her skills were either Holy-type damage and Nature-type damage.
