Vriska's the mythic bitch,  plain and simple. She's rude, cunning, and manipulative, with an egotistical complex. Despite all this, she manages to develop a crush on at least a few characters and at least a few tender moments. Vriska is /definitely/ a belter, though she's probably more of a strong/alto-heavy belter than a mezzo mixer like Terezi. We're looking for STRONG belting, full powehouse voices.

Heather Chandler is an obvious choice here. But go wild belting out any of your favorites! Other good options include:
[Defying Gravity]
[I'd Rather Be Me]
[Dance: Ten, Looks: Three]
PS. I'd stray AWAY from Regina George material. It's far too sultry for anything Vriska would sound like.