What do I do if I don't like talking to someone?

This feels like a really dumb question lolz cuz wdym I need to talk to someone :P. But heres the thing, theres this girl: Im gonna call her B and shes my step sister. Shes young and kind of cringy but thats not why I don't like talking to her. Shes very emotionally relyant on me and I just can't get that attached so its sooooooo draining T^T. Shes really sweet and dosent under understand that I don't really like her. I know this is really mean and I don't have a reason to dislike and by no means do I hate her, but I'm sick of trying to talk and be her friend its annoying :/. Idk I know im probably in the wrong but what should I do? And don't say just tell her or to ignore her because it's legit impossible unless I move across state lines, shes in my family. Help me please ToT.