Is my sister being overprotective?

My older sister Jan (she's actually my best friend from college. She's 38 and I'm 20) doesn't let me wait outside her apartment at night while I wait for a ride home from my parents...She'll actually stand outside and wait with me. She doesn't let me walk home at night, which is understandable. Jan told me that even though I am an adult, she feels a sense of responsibility towards me when I am with her. Is it because I'm a girl? I have a mild to moderate case of cerebral palsy on my left side, but I have a strong right arm that I could use to slug someone really hard if necessary. Jan doesn't feel sorry for me or anything and she knows I'm really strong. We live in a small town where there is some gang activity, but there hasn't been a murder since '93 or '94.