Because Claudia has really only had Monday as a friend for years, she doesn’t have the skills to make friends on her own. This explains why she asks Michael questions that come off as rude and struggles to connect with him. Claudia is also trying very hard to look mature, which is why she refers to trick-or-treating as kid stuff. But she’s also struggling with Monday’s disappearance, and that seems to be contributing to her awkwardness.