The use of Vampires as a metaphor for human sexuality is one that goes back to the earliest artistic visions of the creatures. It helps that the modern personification of the Vampire begins in Bram Stoker’s penny dreadful, Dracula.

Here we see Stoker (a wonderful representative of the mind state of the conservative Victorian Male) use his rather badly written book as a way to explore several underlying themes about sexuality. And to be precise female sexuality.

It is worth remembering, one of the greatest weaknesses of the book was it’s ability to create this amazing protagonist in the first part (Dracula) and then have him basically disappear for the remainder of it. The horror then focuses upon women.

It is women (the brides of Dracula) who seduce/feed upon Harker when he is trapped in the castle; it is Lucy who falls because of her lustful nature to Dracula’s bite and who comes back as a monster; it is the endless (and boy I mean endless) struggle for Mina (and her desires) that dominates the third part of the book.

The negative imagery of female sexuality in Stoker is not carried to the present day but the idea of vampires/female sexuality being linked clearly is. We see it expressed in various ways from classic Bella Legosi era black and white flicks (1936’s Dracula’s Daughter fits right in here, but he was not in that one), to the soft-focus female victims of the Hammer era, right up to the modern, where True Blood, Buffy, and several others explore the seemingly forever tied link between vampires and sex.

As such, it becomes no surprise that along the way the whole thing includes female sexual empowerment as personified by same sex desires. At times done by men for pure titilation and objectifying (several Italian horror movies from the 70’s come to mind) and other times as attempts to express female empowerment.

The direct link between female same-sex relationships and vampires really begins not in literature but in cinema, with the exploitive European fashion for using Vampires as a way to basically film soft-porn which created a global desire for such films. So you have the likes of 1970’s The Vampire Lovers, and La Vampire Nue; by the next year you had Countess Dracula, The Velvet Vampire, Les Frisson Des Vampires, Lust for a Vampire, Daughters of Darkness and of course, Vampyros Lesbos. The market seemed to calm down a tad after that but notable mentions must go to The Blood Splattered Bride (1972), Levres de Sang (1975), Fascination (1979) and of course The Hunger (1983).

Simply? The link between lesbianism and Vampires was truly born during the 70’s cinema to commercialise sex for the big screen; if that feels a little seedy, then I cannot but agree.

I will concede the ground if someone wishes to explore a more mythic route towards explanation; while I have studied the portrayal of Vampires it has been entirely from the context of the history of cinema as opposed the cultural/ethnic history of the creatures.

One of the earliest examples that can be read as codifying, at least in part, the Lesbian Vampire trope is in Le Fanu's 1872 piece, Carmilla. In terms of the literary and historic readings of this text various scholars have noted the erotic and lesbian themes present.

• Jan Perkowski on page 132 of The Darkling: A Treatise on Slavic Vampirism notes of Carmilla that 'Carmilla feeds by puncturing the victim's breast and drinking blood. She also strangles young girls in their beds.... The erotic (lesbian) theme is all-pervading: the vampire yearns for sympathy and consent; it either protracts its enjoyment and sustenance like an epicure or overpowers its victims with violence to exhaust her in a single feast.'
• Ken Gelder in Reading the Vampire (page 60-1) argues that Carmilla 'mobilises a range of undercoded but no doubt recognisable representations of the aristocratic lesbian'. Gelder also gives a brief reading of Victorian positions on female homosexuality; 'The Victorian view of lesbianism conventionally saw it as 'unnatural', against nature... [However] the story is fluid enough to eroticise same-sex relations in ways which do not appear unnatural and which do not produce horror or fear.' There's also a brief historiographical contextualization of queer theory and the lesbian vampire.
• Elizabeth Signoretti argues in Repossessing the Body: Transgressive Desire in "Carmilla" and "Dracula" that: 'In "Carmilla" Le Fanu chronicles the development of a vampiric relationship between two women, in which it becomes increasingly clear that Laura's and Carmilla's lesbian relationship defies the traditional structures of kinship by which men regulate the exchange of women to promote male bonding. On the contrary, Le Fanu allows Laura and Carmilla to usurp male authority and to be stow themselves on whom they please, completely excluding male participation in the exchange of women, normative as discussed by Claude Levi-Strauss and more recently by Gayle Rubin and Eve Sedgwick. Stoker later responded to Le Fanu's narrative of female empowerment by reinstating male control in the exchange of women. In effect, Dracula seeks to repossess the female body for the purposes of male pleasure and exchange, and to correct the reckless unleashing of female desire in Le Fanu's "Carmilla.
• Amanda Hobson's piece DARK SEDUCTRESS: The Hypersexualization of the Female Vampire, discusses more recent representations of the hypersexualised female vampire but posits that modern iterations are indicative of 'patterns established in Carmilla and Dracula, in which the female vampire illustrates historically specific and continuing cultural fears about women’s sexuality as well as the titillation of the sexually voracious, beautiful, but deadly seductresses. The image of the female vampire emphasizes cultural obsessions with manifestations of women’s bodies and sexualities.'

[Edit] As a brief reading list I'd say take a look at:

Case, Sue-Ellen. Tracking the Vampire. Differences: A Journal of Feminist Cultural Studies, 3 pp1-20

Gelder, Ken. (1994) Reading the Vampire. London: Routledge.

Hobson, Amanda and Anyiwo, U. Melissa (eds). (2016) Gender in the Vampire Narrative. Rotterdam: Sense Publishers.

Keridiana Chez, “You Can't Trust Wolves No More Nor Women": Canines, Women, and Deceptive Docility in Bram Stoker's "Dracula". Victorian Review, Vol.38 No.1 (2012) pp.77-92

Perkowski, Jan L. (1989) The Darkling: A Treatise on Slavic Vampirism. Slavica Publishers, Inc: Columbus OH.

Dejan Kuzmanovic 'Vampire Seduction and Vicissitudes of Masculinity in Bram Stoker’s “Dracula” , Victorian Literature and Culture vol.37, no.2 (2009) pp 411-425

Talia Schaffer "A Wilde Desire Took Me": The Homoerotic History of Dracula. ELH Vol.61 No.2 (1994) pp.381-425

Signorotti, Elizabeth (1996). Repossessing the Body: Transgressive Desire in "Carmilla" and "Dracula". Criticism, Vol.38 No.4 (1996) pp.607-632