I don't know how to add a spoiler tag so here we go
SPOILER
She is actually the late empror's child (or something). She is related to the FL, part of the royal family which is why she has the same mark on her hand. When she finds out she isn't the real daughter she backs out and feels bad for the FL. So yes she isn't evil and doesn't mean any harm.
i think i read somewhere before that the villain family knew who she really was but instead brainwashed/gaslighted her into thinking she was truly the current emperor's missing child
and since she's still a child, she believed their words and that's why she acted that way; i just haven't seen any spoiler on how they found out that she's just a relative though
yeaaah, but it'll take a while before whole truth gets uncovered
but the gist is that she's not innately bad, just heavily influenced by the gaslighting of the toxic evil family that made her think that's how she should behave as the "princess"
anyways, some spoilers say emperor still treats evie more preciously even after fake daughter starts staying in the palace so at least we have that

THE STORY IS SO CUTE PLS PLS PLS FUCK THAT FAKE CHILD PLS I HOPE THE MAJESTY WONT FUCKING BELIEVE THAT FAKE CHILD AND DANCE W EVIE AT THE AUTUMN BALL