The need to double post makes me pathetic, I know. I just suddenly got reminded of one of the "I'll Obtain Happiness" anthology stories where the "heroine" was a schemer who screamed at the MC for "taking" the man she really wanted. She then got assassinated in a narration box but she was unstable as all get out.
So... upon closer inspection, I'll get off my horse and agree with the majority. Giving the sister a curse like the father got wouldn't be enough. She is a danger to Eliana and needs to be put down.