Being shy and socially awkward also has its benefits. Introverted people usually tend to pick up on other people's energies, that's why they get easily tired in social situations. I'm like that too. But that's why we are also so intuitive and often have a good understanding of others. Maybe you are like that, not only your sister. So don't be too harsh on yourself if you are not a social butterfly, because you can have other great values and skills. :)