Bloodlender - The Bloodlender Trilogy, #1

An ancient magic. A secret garden. A deadly curse. Haunted by her father's unsolved murder, all sixteen-year-old Sophie wants is to keep a low profile. Instead, there's a dangerous magic stirring in her veins. and she has no idea how to stop it. After she accidentally puts her mother in a coma, Sophie is forced to move in with the elusive Delville family, whose historic French manor holds secrets even darker than hers.
Their son, Gauthier, is dying from a mysterious illness, while deep in the abandoned garden, old ghosts are stirring. As she struggles to control her powers, Sophie learns that she is Gauthier's last hope. But when new evidence about her father's death threatens to shatter their growing bond, she faces the ultimate dilemma: get revenge or save the boy she's falling for..that is, if her blood doesn't kill them both first.