She is based on the infamous serial killer in history, Countess Elizabeth Bathory.
The story goes.... Mircalla Karnstein was a countess in Styria of then united Hungary - Austria. Born in a wealthy upper class family, she was turned into a vampire by a woman who she called " mother " at age 16- 18. She was from the very infamous Karnstein family who were ill reputed for torturing and abusing people and deep into black magic practice. The Karnsteins didnot have morality. Mircalla was no different. After people found out she had turned into a vampire the locals all staked and beheaded the graves of every Karnstein there was except Millarca's. The reason was one man. A Moravian gentleman was madly in love with Millarca but it was one sided. The man however,upon learning of Mircalla's vampirism, hid her grave far away where no one would find it and stake her, all out of love. Hundreds of years later, Mircalla would come back to haunt Laura just like many other girls. Carmilla had interest in women only in the original fiction novel although Elizabeth Bathory herself was straight with a husband. Unless Carmilla had a man to manipulate for ulterior motives, she never found men attractive despite having many suitors and being very beautiful.
Mircalla is Millarca and Millarca is Carmilla.
Carmilla is a gothic novela written by author Sheridan Le Fanu in 19th century. Carmilla predates Draculla. This is ultimate canon.
A wonderful fact is that the Bathory family and Draculesti family were relatives and allies more or less in antiquity.
