Lidia was the only daughter of Valerian's count. She was a cheerful little girl, until she was kidnapped and murdered at the age of six. 
High priest of Ninurtah brought her back to life, but after that she changed. She became quite and spent most of her time with her books, alchemy labs and magic practices. 
She remembered almost nothing about her death, so they never found a murderer.
At her sixteen, Lidia left home, and spent a few years traveling.
After recent death of her father, she returned home, as now she is the countess Valerian.

Most of her people still not sure about Lidia. 
She has already showed, she's all far from being naive, some still believe she's too young to rule.
There also some rumors about her journey, which, according to that rumors was somehow very different from ordinary "nobleman's journey".
So people often calling her "our dark lady". First it sounded more like a joke. But now there seems to appear some righteousness in this nickname.