Sisters are bound for life. And while it's not a given that your sister will turn out to be your best friend, when it does happen, consider yourself very lucky to be a part of this magical relationship.
Be proud of her accomplishments no matter how small. Be objective and give each other constructive advice. Learn from each other’s differences and share your deepest secrets.
Love your sister unconditionally. Continue to experience life together because she's your best friend and you'd be lost without her.