Alex Bishop is an agent of the VIA.
That is the Vampire Intelligence Agency.
If you knew to look for it, and being human that is almost certainly not the case since the VIA was extremely hush-hush, you would head to London and the office building housing a large legal firm. That group of successful lawyers was not the spot, though, as you would have to go to the two floors above those it held, seeking out Keiller Vyse Investments. That is where you would find "the nerve-center of one of the world's most secretive organisations, operating under the auspices of a worldwide Federation whose existence was known only to a very select few."
The VIA was "the Vampire Federation's security wing, set up to police its hundred thousand or more members across the world". The Federation was the "embodiment of the modern age of vampirism" while the VIA's role "with its global empire, working under the watchful eye of the Federation Ruling Council, was to control the registration of new members and enforce the three laws of the Federation". These were: "1. A vampire must never harm a human. 2. A vampire must never turn a human. 3. A vampire must never love a human."
Enforcement of these laws fell to field agents like Alex Bishop. "As a lot of renegade vampires had found out the hard way", "when they stepped out of line, she moved into action".
When we first meet her she shows us this action as she is going up against a nasty killer who had just viciously slain two innocents and was about to feast on a third; his blood lust turning to Bishop as he claimed she would be next. She wasn't, as her specially configured Desert Eagle automatic showed. The bullet that the weapon firing made would not stop a creature like this with its amazing healing capability but the anti-vampire poison it carried, Nosferol, definitely could. Bishop tells the one remaining human that "it takes a vampire to destroy a vampire properly".
Bishop in action proves a statement made by one of her superiors about her, "Cook as a body on ice, hotter than a chili pepper". The fact that the man's comments were not made as a compliment but snidely as they did not get along does not make it any less valid. Bishop is cool under pressure and extremely good at her job.