The Dragon Queen: Truth Unknown

Cleo Arcangela Heath was a normal 16 year old, with a normal loving family and normal friends.

Note how everything's in the past tense.

After the murder of her family, a drastic changed happened to Cleo. She joined the SAC, the Supernatural Assassin Council. She shut down all her emotions towards others, except her closest friends. She turned into a ruthless killing machine, becoming the top predator of Asia. She's known as 'The Dragon Queen', since the last thing her victims see is her Dragon tattoo which glows red, signalling the ending of a victim.

But when she's sent to England on a mission to kill a pack of dangerous drug dealers who happens to be vampires, she meets Ryan Miles, 'The Viper', the most dangerous assassin in England and America. But to Cleo's horror, he works for the Boss of Silver Arrows, the group that killed her parents. Will she get her revenge or will love conquer her heart?