The Vampire Diaries has founds it Greta.

Former American Idol contestant Lisa Tucker, who finished 10th on season five, will debut next month as Luka's sister, the young witch Klaus has been reportedly holding hostage.
在《美国偶像》第五季中获得第十名的选手Lisa Tucker将会扮演Luka的妹妹Greta,并在下个月播出的剧集中首次登场。Greta是Klaus用来威胁巫师Luka父子的人质。

Greta will appear in at least two episodes, but we’re hearing that she may actually appear in four — including the big finale.

Greta will first show up on April 21, the same installment during which we'll meet Joseph Morgan as Klaus. Her magical character is described as "cool, hip, smart," and "a bit of a thrill-seeker."
Greta将会在4月21日(美国时间)播出的那一集中首次登场,和Joseph Morgan扮演的Klaus在同一集中登场。她的性格可以用“酷、潮、聪明,还有点儿爱找刺激”来形容。