And she still doesn't know who struck the Abraham Lincoln High School freshman - known to classmates as "David Cool" - the night of April 3, while he was riding his bike on Tyson Avenue in the area of Ditman Street about 10:15 p.m.
The sole witnesses to the collision, two teenage girls, gave only a vague description of the car - small, dark-colored, maybe four doors. Police said they have interviewed neighbors, reviewed the one available surveillance video, and followed up on tips about cars matching the description, but to no avail.
"For now, the best thing I can hope for is someone was there and saw who did it, or someone has a guilty conscience," said Accident Investigation Officer Daniel Shead.
Without that, the best remaining lead is David's memory, Shead said. But after a traumatic brain injury, he said, "a lot of times people don't remember anything."
The possibility the driver will never be identified has unnerved and angered David's family, which is convinced he was targeted after a fight with another teenager.
Police believe the collision was an accident based on the accounts from the teenage girls, who said David, who was not wearing a helmut, was texting and cut into the street when he was hit.
They also said the car kept going east on Tyson but did not speed off, Shead said. He said he suspects the driver was drunk.
But Robbins doesn't believe her son, an experienced bike rider, was texting. She said she has received conflicting information from police and worries that her son was attacked, saying rumors about the incident have circulated through her neighborhood to the point where her younger son can't leave the house without someone asking, "You know who did it, right?"
"It's hard, because I want justice, but it's not knowing," Robbins said. "Do I really want to know what happened?"
She could handle knowing it was an accident, she said. "But I can't live with knowing somebody intentionally did this to my child."
Rushed to the hospital after the crash, David, who suffered severe head injuries, was not expected to live, and for weeks, he was unresponsive. Robbins said doctors advised her to take her son off life support, saying it was selfish to keep him alive when he had little chance of improving.
Did they know with 100 percent certainty that David wouldn't recover? Robbins asked.
They didn't, she said. She told them that then, there was no choice to make.
David made progress in the hospital, responding first to a request from his sister to move his hand. By late August, doctors suggested it was time to move the teenager into a nursing home.
But Robbins was determined to bring her son home.
"I don't care how hard it is, we're going to do it," she recalled telling the doctors.
Now David is beginning to breathe on his own for three hours a day, and doctors hope to wean him off the ventilator, Robbins said.
He can high-five his friends when they visit, and he blows kisses to his girlfriend, Sandra Szydlowski, 17. Robbins, who has three children, quit her job as a manager of an auto parts store after David was hospitalized and she was placed on leave without pay. Insurance pays for visits from nurses, who spend 16 hours during the day and night with David, but Robbins said they don't always show up.
Robbins also has been unable to get outpatient therapy for her son. So she and her family try to stimulate his mind, asking him questions - he can nod yes and no - and carrying on conversations as normal.
But their memories of seeing his injuries for the first time haven't faded, and neither has their worry and anger over what happened.
"It makes me so mad, just thinking about his face," said 15-year-old Louis, his eyes fixed on the dining room, his brother's bed visible behind a thin sheet hanging in the doorway.
He often tries getting his brother to sit up, prompting him with a count of three.
"I just want him to get up and go," Louis said. "I want him to just be like, 'I'm OK.'"
Anyone with information about the April 3 incident is asked to contact the Accident Investigation District at 215-685-3180, 911, or through the Police Department website.
Contact Maddie Hanna at 215-854-2771 or firstname.lastname@example.org