because she is Eunhyuk's step sister and now she is an adopted sister of Suae.....in both cases the blondie is an illegitimate kid therefore she is jealous of both of them. And since the two of them had always sympathized with blondie, she thinks that she owns them and everything related to them.
why does the author keep including the blonde girl? (her actions always seem fuzzy and out of place) ( ̄へ ̄)?