This made me curious about you now. Do you get along with your mother? Did you as a kid/teen? You're free to not answer if you don't want.
I understand where you're coming from and in most cases would agree, but in Sins case, I don't think it would be helpful. Sin has bigger problems to focus on right now, than appearances. I doubt her mother is trying to deal out harsh truths for Sin's own good. I suspect she's merely shallow. That is how a shallow person would naturally respond to something like that. And obviously Sin isn't taking a valuable lesson from this, it's just heaping more stress on her and further damaging her relationship with her mother.