In essence, they're the same, in spite of the years spent denying it and coloring hair and makeup and ridicules clothing; all the years spent cataloging all the things her sister is and turning herself into all said sister isn't have done nothing to change the fact that they are alike. It's obvious, physically, how alike they are; same hair, eyes, nose, mouth, body – they have the same movement, even, and people are constantly confusing them. (which is just so hilariously stupid, because they're not even twins; their just sisters and if it was left up to them, not even that) And personality wise, they're both stubborn, both ridiculously loyal to the point that they would kill for the people they love, they're both 'musically challenged,' and neither of them can write an essay to save a life.
When anyone confronts either sibling about any of that, they'll launch into a full blown rant, furiously listing all the things that are different between them; the younger will declare that she has lighter hair, lighter eyes, darker skin; that she is more social, more friendly, etc, etc. The older sister will patently explain to the accusing in question that anyone who couldn't see the obvious differences between them 'Is a frivolous nitwit who won't pass high school.' The oldest is studious; the youngest couldn't care less about those sorts of things and concerns herself with 'more important' matters such as boys, and the latest trends while the oldest feels that 'if she wants to concern herself with boys and fashion and resign herself to a life of passive, pointless shallowness, she can feel free to do so.' The youngest is constantly barging into her sisters room and 'fixing her sham of a closet' (i.e. donating cloths to goodwill or throwing them in the dumpsters), and the oldest writes on her sisters clothing things like ''look at my boobs' or 'too tight' and 'this is not a dress, and it's barely even a shirt' in a clashing color sharpie.
(but in essence, they're the same)