beta
In her eyes her younger brother died and her mom basically "abandoned" her then adopted a baby boy, appearing on interviews and events together all lovely and what not. Now that kid is calling her noona smiling like nothings wrong ofc she'll feel negatively towards him. Not to mention she was probably raised as a spoiled chaebol brat.
You can't honestly expect the kid to rationally think "oh it isn't his fault! I shouldn't be taking it out on him!". She also clearly told him not to call her noona again and judging by how patient Gongja is being he also gets it. The kid isn't a bch she needs therapy.
Be evil until the end it just makes everything more satisfying
Hahaha for real!