Foundation: Since the humans lost the war, they are forced by the Blood King to be incorporated into the vampire way of life and serve under them. They decided to rank each human into different level of slaves since the vampires themselves have their own social class. Higher ranking slaves are given to higher ranking vampires as they tend to match better.
Note 1: For a human to be considered a high profile slave they have to either be extremely beautiful or handsome, have a high level of high quality blood, or have been previously high social status during the period the humans still reigned.
Note 2: Vampire servants exist as well who serve under their respective Vampire Lords. They are different from human slaves as they are paid with money while slaves are paid with food and shelter only.
If you have all three, even better. In other words if you are a former princess like our FL, you are considered extremely high profile.
Slave Ranks:
Royal Crimson - Humans who are deemed extremely valuable and sponsored by the Vampire King himself receive this title. Only Grand Dukes and Dukes are able to have human slaves of this quality. These humans tend to be ones of former royalty and are known for their attractive looks, strong abilities, high quality blood, etc.
Crimson - Humans with this title are still considered pretty high profile. These humans tend to be former nobility and are still considered usually pretty attractive. They are known to be valuable for their abilities with intelligence, labor, etc. They tend to also have good quality blood.
Red - Humans with this title are the average slave to a vampire master. They have no connection to any previous high ranking status during the human era and nor do they stand out for anything special. They just mainly are there to act as a blood source for their vampire masters and to do simple tasks.