Catherine is a beautiful seventeen-year-old girl. Having rarely left Brooklyn, she's incredibly naïve. She finds it hard to stand up to her father figure, Eddie, because he's done so much for her over the course of her life. He's all that she knows. She tells Rodolpho, "I can tell a block away when he's blue in his mind and just wants to talk to somebody quiet and nice" (2.57). That's just it. That's how she sees herself – "quiet and nice." That's who she wants to be.
Catherine is often accused of being one note, of lacking complexity. That may be true to a certain extent, but it's undeniable that her character changes over the course of the play. In the beginning, she's exactly how we've just described her. However, as the story rolls along, she does find the nerve to stand up to Eddie. She defiantly dances with Rodolpho right in front of her uncle. Eventually, she even finds the guts to tell Eddie she's leaving to marry her Italian lover. Of course, Eddie has done some pretty crummy things to her by this point. Still, though, she could've remained weak and submissive, allowing him to have his way. Rather than being the biggest doormat on Earth, she chooses instead to stand up to him and live her life the way she chooses. That's two notes at least.