@Gadriel I can understand where you are coming from... however, her being born into the blood flame cult is reason enough for her evil acts. Your being is shaped by the influence of those around you, especially when you're young. Obviously her view does not align with the MC right now. However, what she is doing is not considered incorrect or "evil" where she lives, rather it is the norm. So sure, I agree she must change in order to be with the MC, however she doesn't necessarily need a "justifiable reason" for her evil acts.
I'm just here for a good time 
