This film is a combination of the Universal Studios 1931 version of Dracula and J. Sheridan Le Fanu's novella Carmilla.
Countess Zaleska is a typical female vampire: she uses her beauty as her most powerful weapon, and it works on both men and women. While Countess Zaleska has both male and female victims, much more screen time is given to her seduction and killing of Lily than of the anonymous male passer by that she does away with earlier in the film, putting special emphasis on her "sexual deviance." And she casts a similar glamour over Janet Blake in order to compel Dr. Garth to do her bidding. As she waits for Dr. Garth, an unconscious Janet as her prisoner, Sandor comments that she won't be able to wait long, implying she will have an unstoppable urge to make Janet her victim in ways to horrible to be represented fully in this film, made when the Hayes Office controlled what was shown on the screen. Dr. Garth interrupts what is set up to look like the beginnings of a lesbian kiss, where Countess Zaleska is straddling the prone Janet. Countess Zaleska also has fewer supernatural powers than does a male vampire. She may be able to turn into mist for short periods of time (this is how she got into the jail to retrieve her father's body at the beginning of the film), but she can't truly shapeshift, and doesn't even exhibit the superhuman strength possessed by some other vampires, male and female. Her sexuality and ability to mesmerize with it, and her ability to cheat death are her only true supernatural powers.
Countess Zaleska is also decidedly Eastern in appearance. When she goes out in public, she wears a hooded cape in such a way that she resembles a veiled middle eastern woman who looks quite out of place in modern England. The ring on her finger that she uses for hypnosis is a sort of third eye.
Yet for all her being a femme fatale, Countess Zaleska really only wants to be under male control. She wishes to be under the influence of Jeffrey Garth rather than her deceased father, who represents the forces of darkness. This way, she can live the life of a woman (what is she now?).
Good vs. bad aristocrats. Countess Zaleska is contrasted with Jeffrey Garth's girl Friday Janet Blake, who is a baronet (he mentions this in passing during their quibbling as she drives him back from Scotland). Although Janet is a baronet, she 's not too good to work, and further, do work that puts her in a position subordinate to a male professional. And Jeffrey, as a psychiatrist, is a new sort of nobility. His patients are mostly noble women, and from the way he talks about them, he believes their disorders are due to hysteria or an excess of free time rather than legitimate mental illnesses. Countess Zaleska, on the other hand, behaves more like an aristocrat. She knows how to treat Dr. Garth, who is after all a paid servant. He must come see her, or if she is to see him, it will be on her own terms, at night. She also feels free to not follow doctor's orders.
Countess Zaleska is evil not only because she is a vampire, but because she is an unruly woman, one who controls men rather than submitting to them. Her outdated sense of class privilege provides one explanation for her behavior. She outranks nearly everyone on the film, and comes from a time where aristocratic rank was all. But she can also use her sexuality to get men to do her bidding. Sandor is a sort of "wife" to her. He helps her dress and takes care of all her other intimate daily needs. Furthermore, he's led on with a promise of permanence. Countess Zaleska has promised him eternal life (sort of like a man promising to eventually marry his live in lover), but of course she never seriously meant to honor this promise. The class differences between them are too great, he's not very attractive, and why buy the cow when you can get the milk for free?
Science vs. Magic: Science is associated with men and rationality. Magic is associated with women and the irrational. But what is science but magic that works? Dr. Garth represents science in this film. As a psychiatrist he practices a medical specialty that attempts to understand and control human behavior. But Countess Zaleska is able to control human behavior through magic. When she has Janet in her thrall, Dr. Garth cannot break the spell without killing her since this is something far older and more powerful than a similar tool he uses, hypnosis. He is thus left at the Countess' mercy, and would continue to be so if she were not killed by her faithful servant Sandor.