She is helping him out so I don't think she had a probelm, it just maybe so sudden and suprising to hear that her brother is gay
She dont care hes gay shes annoyed because he hasnt come to her to tell the news despite how obvious he is. As a younger sister i realized that many times my older sisters were mad at me not because of what ive done but because i didnt come to them. if you dont, they might feel like they are doing a bad job being an older sibling yk plus the fraternal instincts and how sibling dynamics work also plays a role in this. She loves him, she just pissed off cuz he is not straightforward.
I hope the sister ain’t got nothing against her brother being gay cause she seems so annoyed with the fact lmao