What was said by my mother a long time ago is still bothering me?

I'm sorry your mother said this to you it wasn't right, I suggest you confront you mom but not in the manner where it might make the problem worse. It could be that your mom was not meaning appearance wise but in your heart you were being ugly at the time.Also as kids we all say things we shouldn't say have you asked your sister to forgive you, I suggest that as well and let the healing begin.