Night World, No. 2 by L.J. Smith

Includes:
Book 4 - Dark Angel
Book 5 - The Chosen
Book 6 - Soulmate

Vampires, werewolves, witches, shapeshifters -- they live among us without our knowledge. Night World is their secret society, a secret society with very strict rules. And falling in love breaks all the laws of the Night World.

In Dark Angel, Gillian is saved from drowning by her guardian angel. Only visible to Gillian, Angel will fulfill her heart's every desire. But when Angel starts making strange and sinister requests, Gillian must question who he truly is and where he came from.

Armed with a wooden stake, martial arts, and the will to resist a vampire's mind control, Rashel struggles to avenge her mother's death in The Chosen. Then she meets Quinn, her soulmate, who is part of the world she has vowed to destroy.

Hannah receives notes warning her of incredible danger in Soulmate. But if death is her destiny, is the Lord of the Night World's love strong enough to save her?
 
- Goodreads Summary