SHOULD I MOVE ON, IS THERE ANY HOPE?

Well I like my friend's sister but she is very shy around me. I like 4yrs older than her. I don't know if her shyness is because she is either disinterested or she looks at me like i am a suitor. Well in beginning I found her interested in me also asking her bro some questions about me. Yet for the last couple months I realized she doesn't talk to much with me. I would text her 3x one day and she didn't respond till 3hrs later. (I think that might annoyed her texting her all that much) Recenlty, I texted her wishing her luck on her LSAT and she didn't respond either. I don't know what to do when I see her, when I hang out with her bro. Should I just give it some space and revisite it or move on?