It may help that vampirism gives both the length of time and the stakes to make melodramatic behavior of the leads believable motivations. Mother vampire seeks a quiet life of transient prostitution to conceal her daughter from an ancient threat she has never fully explained to the girls. Daughter seeks a more refined and respectable lifestyle and yearns to tell someone, perhaps her new quasi-boyfriend, the truth about who she really is.
Both backstory and current conflict come to a crux on a dark pier, where both heroines will be either destroyed or transformed.
See also