I feel like my older sister always outdresses me?

Alright so I am 15 and my sister is 20. I am one of those people that LOVES fashion and wants to be a fashion designer and everything. So anyway, I am usually the one around town and in school that is always best-dressed and people tell me that all the time. (I am NOT being conceited, I am just telling you other people's opinions.) But when my sister comes home, I just get panicky with everything I wear. And its also with my future-sister in law (Will become my sister-in-law in like 5 days) and we are helping her out with her wedding and everything, and she is 24 and she always looks great so I want to look really good on these days. I just feel like they always outshine me. and they don't even try to. Like today, we are going on an 8 hour car trip to get to the destination of the wedding and I am in sweats and a t-shirt because its just a car ride, and my sister comes downstairs in these really cute capri running tights, and and cute t shirt and then over it a really cute plaid button up shirt with a cute necklace and her hair is curled. Like what?! We are just going in the car! And everytime she comes home from college she has like a gazzillion new shoes and outfits with her. I do'nt have a job, I just babysit and dog walk and thats not that much money so like I usually have to buy my own clothes because my mom believes it gives me appreciation for money. So yeah, I just feel like she outshines me. And we both shop and the same stores like charlotte russe and forever 21 and american eagle and maurices and gap, but still I just can never top her outfits. She is perfect. And people are always like "oh! your sister is so pretty!" when she is around and when its only me they are then like "oh your so pretty!" I JUST DON'T UNDERSTAND! does anyone else feel this way with their older sisters? And it doesn't help that out of the four kids she is the favorite. My parents love her. and my brothers and I talk about it a lot cause its annoying.....