Tanya Sellers wonders, "What if?"
She cried when she talked about the shooting that killed Pendleton and injured her son Lawrence.
Lawrence Sellers, 17, is going to okay after being shot in the leg alongside Pendleton at a Kenwood park on Tuesday.
He is struggling to come to terms with Pendleton's death, according to his mother.
This surveillance video obtained by ABC7 News shows several young people running after shots were fired and officers arriving at the scene.
Sellers said her son's friends returned to help Pendleton.
"These are good kids who just wanted to enjoy a break in the weather, and this happens. It makes no sense," Sellers said.
People with information about the crime must come forward, Sellers said.
"Please tell the police. This is becoming ridiculous. Chicago should be on the news for something wonderful, not the fact that we're killing children, our own children, at a very rapid rate," Sellers said.
The unidentified shooter or shooters remain at large though police have been getting tips, according to Chicago Police Department Superintendent Garry McCarthy.
"We have to run down every single one of those tips now and see which one is going to prove fruitful for us. There's nothing to report at this time," McCarthy said.
Chicago Mayor Rahm Emanuel met with the Pendleton family Wednesday evening.
"As we grieve for Hadiya, we need to work together to protect our greatest resource, the children of the City of Chicago," Emanuel said.
No one in Pendleton's group was in a gang but they may have been mistaken for rival gang members, according to police.
When Pendleton was a 6th grader at Woodson Elementary School on the South Side, she appeared in an anti-gang violence video.
"So many children out there are in gangs, and it is your job as students to say no to gangs and yes to your future," Pendleton said in the PSA.