When her mother asks her about Romeo, Juliet responds with evasive answers. She says that he is "a gentleman," but she does not say that she loves him. She also says that she does not want to marry Paris, but she does not say that she wants to marry Romeo.
Juliet's ambiguity is a way of protecting herself. She does not want to get her mother's hopes up, but she also does not want to anger her. She knows that her mother will not approve of Romeo, so she is trying to avoid the subject as much as possible.
Juliet's ambiguity is not a sign of fickleness. It is simply a way of dealing with a difficult situation. She is trying to be loyal to her mother, but she is also trying to be true to her own feelings.