So i need opinions on this! should my sister get the car for the summer?

yes well life is a lot like that, and just think, most kids do not even have one car, let alone the chance to share. You know what is going to happen every year , and all you need to do is save your money and buy your own car, Its a shame your sister has no heart, otherwise she would let you use the car when she was not using it. but sitting in the shadow of your sister sucks, so do what you need to do to get through this situation, you should be leaving home soon for college anyway and this problem should solve itself.