Around 2015 to 2016 I started a novel about a girl who was transported to a parallel world and took the place of her parallel self. In this world, they practice magic. She takes her evaluation test soon after and is revealed as pretty much trash.
She struggles with her studies in the magic academy for a while, and then takes a second test, where it is revealed that she actually has two souls that control different aspects of magic, after which she becomes very powerful. I think her aspects are something like darkness & lightning, with lightning being a super-rare, strongest attack-type aspect.
She moves into a better dormitory with two friends, and then they have to find some more people for some kind of monster-hunting exam or something. That's as far as I got, I think.
I also remember her often mentioning how tall she was. It felt like the author's pet-peeve.