Thank god they gave the villain at least a little bit of depth.
EDIT: Y'all clearly hate Sandra which is (mostly) fair, but please just consider this -- she grew up in extreme poverty with abusive parents that denigrated her and stole from her earnings to buy wine and luxury items instead of food. Of course she's gonna ruthlessly be a social climber, because she needs funds to survive.
I still intensely dislike her for manipulating the prince and Evan, and making the elder prince and the younger servant ill, but, as far as we know, she isn't using her magic intentionally because she doesn't know that her persuasion is due to (dark) magic. I can't really blame her for doing horrible things, if she's not doing them intentionally. Someone needs to clean her mouth out with soap though and teach her some humility.
As for the fire scene: She didn't set the fire. She didn't block her family members from leaving. She just refused to help. Is it mandatory for you to help the people that made you suffer for 16 years? The people who stole from your paychecks and made you resort to thievery to feed yourself? I don't think so -- she's under no obligation to try to save them. Not saving her younger siblings is less justifiable, but I don't think not helping someone makes you a bad person -- especially when that could make it harder for you to survive in a dangerous environment like a housefire.
Again, overall, she's still a pretty bad person because of her arrogance and the harm she's caused (though mostly unintentional or due to inaction), and especially because she faked an assassination to raise her social status, but I think the above is worth considering before calling her "the devil" or saying she should be "impaled and put through medieval torture".