오빠랑 말 한마디에 이렇게 = All this just because of the one word/question I had with you/him. (= 오빠랑 말 한마디에 모두가 이런 방응을 보이다니 = I'm surprised everybody's reacting like this to the one word/question I had with you) 오빠랑(with you/him) 말 한마디에(for one word/question/exchange) 이렇게(like this / this much reaction). It's hard to say exactly without knowing more about the situation, but it seems like she got a lot of supportive responses from people about her question and is reacting surprisedly.