Selene is the main character of the Underworld franchise. Some of her past was revealed in Underworld: Evolution, where it was revealed that Victor commissioned Selene's father to build William's tomb, which is why her family was killed by Victor, to keep it a secret. In the prequel film, Underworld: Rise of the Lycans, they told the story of how the war between the Vampires and the Lycans got started.
In 2011, a 3-part anime mini series called, Underworld: Endless War was released, and it showed Selene hunting 3 Lycan brothers from across 3 different periods of time. Part 1 took place in 1890; and Part 2 took place in 1967. Given how incredible Selene is, should she have her own interquel movie- a prequel to show how she rose to become a Death Dealer in the first place? As well as her first time as a vampire? What do you think?
(References: Underworld- Wiki- Selene; Google Images- Prime Video- Underworld (2003))