lol mine function normally in the society too and may be clueless when it comes to us kids, lol..
nothing to do - is this only a problem in the summer, cause it's the holidays, or otherwise too?
I'd definitely look for any interesting volunteering opportunities or workshops/courses.. You can meet some really cool and fun people that way... And maybe it would even help convince your family you're an okay person?
I'm a terrible person sometimes, so I'd probably start to joke with your sis about this, like 'Beware' or something, though if she has no sense of humor this could be a dangerous thing-?? (My sis and I have threatened to kill each other multiple times, when we were little kiddies, though we always stand up for each other if necessary too.. I don't use those words anymore, though I've heard little kids say it all the time.. It may not mean anything.. Luckily my sis does have a sense of humor!!)
Do you and your sis have any common interests? Like books or movies? Sis and I have different taste in some, like some both though... It could be really helpful if you find something you both are interested in and like to talk about??