10/11/2012 12:05 pm ET Updated Dec 11, 2012

Unite for Girls this International Day of the Girl with Girl Up

She deserves the best that the world has to offer.

"She" is my sister, Melissa, an upbeat 9-year-old at Beaumont Elementary School afflicted with Charcot-Marie-Tooth, a form of muscular dystrophy. "She" is Tigist, a brave Ethiopian girl who was about to be forced into child marriage at age 14. "She" is every girl in the world.

Who do you care about? Is it your sister, your niece, your daughter, your best friend? One girl--every girl. As a Teen Advisor to Girl Up, a campaign of the United Nations Foundation; as a 16-year-old girl myself; but most of all, as an older sister who would literally give my sister the world, I am calling on you to join our movement in the first International Day of the Girl Child on Oct. 11, 2012.

This October 11 marks the first International Day of the Girl Child, designated by the United Nations General Assembly last year. After a two-year campaign spearheaded by Plan International and the Canadian Government, this holiday will be revolutionary in terms of recognition of girls' rights. The day is dedicated to highlighting gender inequalities that remain between girls and boys and addressing the various forms of discrimination and abuse suffered by girls around the globe.

Child marriage is among the greatest and most pressing of these abuses: while internationally recognized as a human rights violation, this awful practice still occurs in developing countries, where 1 in 7 girls are married before the age of 15. Every minute, 19 adolescent girls are married. Nineteen adolescent girls like me or like your sister, your niece, your neighbor.

No matter how much MTV glorifies teen pregnancy and marrying young, child marriage takes away a girl's freedom, health, and opportunity to pursue a better life through education. Imagine being 15, forced to drop out of school to take care of a squalling infant. Imagine being 15 and the mistress of a small household, tethered to your husband and your domestic chores. Imagine being just a girl, who dreams of bettering her life--but can't.

Frequently, girls don't have a choice. Of the 10 million girls that wed each year, many are forced by tradition, poverty, or simply the economic incentive that the "dowry" or bride-price brings to the family. Imagine being a girl, a human being--yet reduced to the price of a few cattle.

We are all girls. We all possess the same basic human rights. We all deserve the same access to education, freedom, and opportunity, whether we live in America or Ethiopia. So I want to call on everyone to make a special effort to recognize the needs of girls. Girls around you as well as girls across the globe in developing countries in Africa and Asia. Girls like my sister or yours.

Luckily, if you're reading this in a developed country, you're in a position to do so. Girl Up gives American girls the opportunity to become global leaders. As a Teen Advisor like me or just as a supporter, we are given the chance to channel our energy and compassion to raise awareness and funds for United Nations programs that help some of the world's hardest-to-reach adolescent girls. And right now, we're calling on you to rally for International Day of the Girl.

I can't cure my sister's muscular dystrophy, but you can cure another girl's poverty, grant her education, and give her the ultimate gift of the opportunity to better her life.

What do we want you to do?

1.) Organize a rally in your area. This can be as simple as holding a meeting at your school or workplace and making a few signs demonstrating your support for girls globally.
2.) Take a picture of your rally and send it to us at Girl Up. We'll be compiling photographic evidence of the widespread support for the rights of girls.
3.) Spread the word on Facebook! In an age where social media is a tool that unites us, why not use it to promote the welfare of girls? Tell your family, friends, acquaintances why you want the girls in your life and beyond to succeed. Share the news of International Day of the Girl.
4.) Give a High Five ($5) at the Girl Up website.
5.) Start a Girl Up Club. Whether it's registering your Girl Scout Troop to help girls internationally or starting a club at your school, create a place where girls can talk about the issues that we still face.

This International Day of the Girl, I am gathering my resources at Conestoga High School to serve girls right here in Eastern Pennsylvania as well as girls in Malawi or Ethiopia--because we, collectively, deserve the best that the world has to offer. Because we have the power to change the fabric of our society.

Because I want my sister Melissa to see a better world for girls.