When Robaba makes a mistake, she clutches an eraser between her lips and rubs away the error - a task she is learning to avoid.
On a recent afternoon, the girl positioned her frail figure before her easel in the sunlit room she uses as a studio.
Robaba's mouth moved back and forth rapidly as she added depth to the face of an Afghan police officer, Serajuddin Afghan Mal, who has reportedly defused several thousand improvised explosive devices left along the roads by Taliban fighters.
This was her first commission, which came after an Afghan MP saw a story about Robaba on a Kabul TV news show last month and contacted her with a request to produce a portrait that would honour the officer.
The subject suits her, Robaba said, because she wants her art to reflect Afghanistan's better nature - to be a reminder that there is still cause for celebration in a country more often paralysed by suicide bombings and the uncertainty wrought by nearly 15 years of war.
"Usually, people are hearing about fighting, explosions and blasts," she said. "If they listen to my story, it's a story of hope."
For Robaba, drawing was initially a response to a lifetime of frustration and loneliness.
Her parents brought her to Kabul from the country's central Ghazni province when she was 3, settling into a largely undeveloped corner of Kabul that sits near a sprawling lumberyard.
They carried Robaba over the neighbourhood's jagged, dusty roads during repeated searches for a doctor who could unfurl her arms and legs and make them work.
The doctors could only speculate about the cause of her condition and, after about five years, the family gave up.
"We lost hope," said Robaba's mother, Masuma. Like many Afghans, she uses only one name.
Robaba spent most of the time inside the house, maneuvering her torso to get around and whiling away the hours as her three younger siblings grew up around her.
When Robaba was 7, she began to resent that her younger sisters attended school while she stayed inside, often alone for hours.
She found a school notebook belonging to one of her sisters and stashed it under a rug. Later, she did the same with two pens.
While the rest of the family was away, she grabbed a pen with her left foot and tried to write.
When that didn't work, Robaba held the pen in her mouth and slowly copied the first two letters in the Dari alphabet: "alif" and "baa."
"For six months, nobody knew what I was doing," she recalled, laughing. "My sister was saying, 'Where is my notebook?' They didn't think I could steal it because I can't use my hands or feet."
But as her writing improved over the years, the teenage Robaba still had no outlet for her frustration.
So she started drawing. That meant enduring the pain that came with firmly and repeatedly guiding a pencil across what became countless sheets of paper.
"I cannot leave the house. I am not free," Robaba said about her determination, her usually playful eyes widening for emphasis. "I have a desire to draw nature, natural beauty. I'm not free to see these things with my own eyes."
Now, what she can see with her own eyes is the possibility of a future beyond the walls of her home. And maybe even beyond Kabul.
An aide to the MP arrived recently at Robaba's home to retrieve the illustration. In his hand was an envelope holding the equivalent of US$72 - a sum that made the young artist's face blush with pride. Robaba signed her name at the top of the drawing and thanked him.
Farkhunda Zahra Naderi, the MP, said that when she saw Robaba's story on television, she recognised an opportunity.
"She's someone who can give courage to other Afghans," Naderi said. "She's actually sending a message: If we have hope, we can try. We can move forward."
Naderi said she is pushing to have Robaba enrolled in school, with an emphasis on art instruction so the teenager can further develop her talent.
She said she also intends to unveil the portrait of the officer at a ceremony to be held in his honour that will double as a public introduction for Robaba.
She's someone who can give courage to other Afghans
Robaba said she hopes to master drawing and then graduate into painting more sophisticated portraits and natural landscapes.
To that end, she stopped talking and went back to work.
As the lumberyard workers outside used a buzz saw to shave fresh planks of wood, Robaba drew a rough sketch of a dove carrying a peace sign.
The effort took about 20 minutes.
When she finished, the dove had a broken wing.
"Flying with a broken wing is art," she wrote over the picture, before glancing around the room with a look of defiance.