Eh, first of all, it would've been better if Sandra was the FL because the usual protagonist who has nothing but "Kindness" going for her is extremely boring, and it would've been even better if they didn't include the "justification" to her wrongdoings, is it so hard to just let the villain be...
Oh no a tragic past... Like every other FL in existence, that's just cheap and lazy writing, boring, and now let's make her even weaker so the great ML can ride in and save her useless self.
Heroine/Villaines switch is the most boring trope, why do you even add "Villaines" in themes if FL is not a Villaines, but a freaking damsel in distress?