Jessica Williams, of the 12000 block of South State Street, died of an asthma attack after witnessing a shooting in Back of the Yards. View Full Caption DNAinfo/Joe Ward

BACK OF THE YARDS — Jessica Williams was given permission by her grandmother to attend a Back of the Yards party Wednesday in honor of her slain cousin.

As always, Ilene Pearson made sure her 16-year-old granddaughter was carrying her "pump" that helped thwart asthma attacks the girl had battled since birth.

But after witnessing a shooting that left two people dead and two wounded during that Back of the Yards party, Jessica died from an asthma attack that started as she ran from the chaos.

"She wasn't wheezing, wasn't coughing, wasn't showing no symptoms" of an asthma attack, Pearson said. "That why I let her go to the party. God help me."

Two people were killed and two others wounded in a shooting in the 800 block of West 50th Place Thursday morning, A 16-year-old girl who witnessed the shooting died from an asthma attack. View Full Caption DNAinfo/Ed Komenda

Jessica was a witness to the shooting that happened near the party in the 800 block of West 50th Place at 12:18 a.m. Thursday.

Four people were standing on the street and sidewalk in the block when someone fired shots at them, police said. The group had gotten into a fight with the shooter before the attack, police said.

As bullets began flying, Jessica tried to run away from the scene. The trauma from seeing the fatal shooting, the adrenaline from her escape attempt and the brutal humidity gripping Chicago caused the girl to suffer a severe asthma attack at the scene, her family said.

She was brought to Roseland Community Hospital, where she was pronounced dead. Now, family members are saying the young and vivacious girl is yet another innocent life lost due to the gun violence plaguing Chicago.

"She wasn't supposed to see that," said Deshaon Smith, Jessica's uncle, said of the shooting. "She never seen nothing like that in her life. Maybe on TV."

The family of Jessica Williams, including her mother (left, with phone), stands outside the family home Thursday. [DNAinfo/Joe Ward]

Jessica was about to be a sophomore at Chicago Vocational Career Academy. She loved fashion and attending social events. Her mother, Sharron Smith, said she was a cheerleader and involved in the junior ROTC program.

"She left behind a lot," Smith said. "She was an all-around good kid."

The shootings happened during a birthday party celebrating the life of 21-year-old Shondell Adams. He died on June 10, 2012, after getting shot by a rival gang member. According to social media, friends celebrate his birthday every year.

On Thursday morning, after everyone had left the party, 70-year-old Curtis Singleton swept and raked empty cans and food wrappers from the street.

"For people around here —if they're alive, or if they're dead — we try to celebrate them," Singleton said.

But this particular celebration turned horrific.

A 33-year-old woman was shot in her neck and taken to St. Bernard Hospital, where she was pronounced dead, police said. A 25-year-old man was shot multiple times in his head, neck and chest and was taken to Stroger Hospital, where he was pronounced dead.

The man was identified as Denzel Childs in Cook County Medical Examiner's Office records. Childs was pronounced dead at 1:20 a.m. The mother of the slain man told ABC7 he was killed after a fight about a parking space.

A 21-year-old woman was shot in her hand and taken to St. Bernard Hospital, and a 25-year-old woman was hit twice in her back and was taken to Stroger Hospital. Their conditions were not available, but they were listed as "stable," police said.

A witness said he saw a man shoot the 33-year-old woman in her neck. She fell near a water spout sticking out of the ground, he said.

A large pool of blood remained on the street Thursday morning.

"The guy who shot her started to walk away, and somebody cold-cocked his ass," the witness said. The shooter fell to the ground, his head hanging off a curb.

That's when another man pulled out a gun and shot the man five times in his head.

"Pow-pow-pow-pow-pow," the witness said.

Jessica, who lived with family in Roseland, witnessed everything, her family said. They resent that the girl with a bright future will forever be known as a witness to a fatal shooting who ultimately died from the trauma she witnessed.

"She was more than a 16-year-old witness," said her brother Dejon Williams. "She was funny. She liked to dress. Her name should be known."

The 25-year-old woman and 25-year-old man were documented gang members, police said.

"[The incident] highlights in a very real way that violence has unfortunate collateral impacts on our communities," said Ald. Ray Lopez (15th).

For more neighborhood news, listen to DNAinfo Radio here: