Winterbourne is never evil. One cannot imagine him being energetic or decisive enough for that. However, in this passage he does think rather severely of Daisy, though, typically, he allows several possible explanations for her behavior.
Having arrived in Rome, Winterbourne quickly realizes that Daisy is not popular among the American expatriates there: she is not invited to their houses, and she is generally regarded as "abnormal." The American community regards her conduct as not absolutely scandalous, but indecorous and indiscreet, and they do not wish for their Italian friends to meet her or think of her as a typical American.
In this passage, Winterbourne is wondering whether Daisy even realizes that she is being ostracized. Perhaps, he thinks, she is too frivolous, unsophisticated, and childish to have noticed. This is his first negative reflection on her character, contained in the sentence quoted. However, he also wonders whether Daisy is aware of what people think of her and is being deliberately defiant by pretending not to notice. In this case, he thinks is possible that her defiance springs from a sense of injured innocence. However, there is another, more negative, interpretation: that she is defying public opinion thorough sheer recklessness and does not care what impression she makes on anyone.