The Muscular Dystrophy Association tweeted "Talk about girl power!" to its more than 13,000 followers Thursday, with a link to the petition. In the petition's comments section, people have said that they or a friend or a child have a disability and that the push is important to them.
"And it made me feel really good," Melissa said.
Melissa loves American Girl, which debuted in 1986 and has sold more than 23 million dolls. She watches fan-made videos of the dolls on YouTube. She wrote a report on the history of American Girl and presented it to her class a few years ago. Melissa was born in Wisconsin, home of the American Girl company. Her Christmas list was a collection of links to the American Girl website.
During the summer, Melissa persuaded her parents and big sister to take her to New York to visit the large American Girl store there. Her family pushed her in her wheelchair through aisles of dolls and accessories.
"It was really fun," Melissa said.
Her favorite dolls are the ones that American Girl creates each year as Girl of the Year, a promotion that started in 2001. Melissa was excited to find out who this year's Girl of the Year was, but part of her was disappointed that it was a blond dancer.
"It's not that we have anything against blond dancers," YingYing said. "But it's a narrative that's been told already. We wanted to bring a new one out."
So the sisters started the petition.
American Girl declined a request for an interview but said in a statement that it was committed to inclusiveness and receives hundreds of requests for dolls to reflect various real-life circumstances.
The company already offers crutches, wheelchairs, hearing aids, and other equipment for children to buy for their dolls. Cancer patients can buy dolls without hair.
But Melissa wants the company's highlighted Girl of the Year to have a disability.
Melissa can walk for short distances, but for longer trips, such as down the hallway at Tredyffrin/Easttown Middle School, she uses leg braces, a walker, or a wheelchair. And while all the American Girl characters face obstacles - such as bullying or loneliness - none has battled physical disability.
Thursday morning, Melissa and YingYing sat close together on a couch in their home, across from the Christmas tree they used as a backdrop for the video of Melissa asking for support that is posted with their petition on Change.org.
Melissa described how she sees other girls climbing monkey bars or running around during recess.
"And I don't get to play with them," she said. "Sometimes it makes me feel lonely."
The sisters' campaign isn't just about having a toy with a disability, YingYing said. Each Girl of the Year is "an immersive experience" and comes with books, games, and a movie, YingYing said. Girls look forward to the big reveal every year.
Although the sisters hope Melissa will be getting a Girl of the Year with a disability next year, they realize their push could take longer.
"There's always 2016," YingYing said. "Or '17."