Sorry, but that was such a stupid move. And just because she didn't like seeing her brother cry.
She could have talked with him to ease his pain, making her presence bigger in his heart so that he can eventually let the heroine go. It would need time, obviously, but it's better than what she did. I mean, almost everyone in the family has already disliked the heroine, which means that their like/dislike can be changed. Even if the brother's love can't be totally erased, it must at least can be lessened.
And yet she decided to render all her previous efforts to gain her brother's trust null instead. She basically admitted to her brother that everything happened because of her manipulation. What do you think would happen when the rest of her family hear that?