First, before even reading the other responses, I have to tell you that if your sister is all those "more" things, but is ACTUALLY pointing out all your flaws, that in itself is a character flaw in her that basically cancels everything out, so don't be jelly
On the other hand, are you sure she's really pointing them out, or does all the greatness you see in her make you insecure so that YOU compare yourself and are critical of what you perceive to be your "shortcomings"?
Sounds like you live at home, so do you drive yet? Driving in the car alone, especially on an easy road without a lot of traffic, is the BEST way to try out singing with NO fear of criticism. If you're not driving yet, maybe you could talk to your band director about getting involved in choir or chorus (don't ask what's the difference because I don't know). I remember as a I'd, my cousin or sister and I would swing just as high as we could on the swing set and sing right out loud, because the squeaking of the swing set and the sound distortion of swinging was distraction enough to take away the fear. Another great way to sing your heart out without fear of being heard (and win brownie points with mom and dad) is to sing while you mow the lawn. Just some suggestions...

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