Crown of Poison and Mirrors

What if Snow White were an assassin and the first person on her list of revenge was Prince Charming?

Infiltrate the Prince's ball, manipulate the mysterious Grand Duke to take down the royal family, and if all else fails, then kill the prince.
The plan seems easy enough, but conflict burdens Brisa's heart. After being recently reunited with her birth family, the last thing she wants is to jeopardize their title of nobility and lives. Can Brisa save her sisters, who are the only family she truly remembers? The torture and pain of the last six years created a bond deeper than blood.
The dastardly prince imprisoned them. Or so Brisa believes for how else could they have disappeared without a trace? Does she assassinate him to save her sisters at the cost of her birth family's lives? Or does she take the risk of recruiting the Duke, who is conveniently her betrothed, and manipulate him to her plight at the risk of losing everything?