Police are now looking for the suspects, who could be very young.
"I can't believe how strong she is," said Shiloh Colon of their friend who was the victim of the attack.
That victim is identified as Diana. For safety reasons, she's not using her last name, but her friends and police say she was the victim of the heinous attack.
"It was such excruciating pain, and I'm sure she went into shock. Immediately," said Colon.
The attack happened at around 1:30 p.m. Sunday. The victim had just gotten off the Market/Frankford Line (also known as the "El") at 52nd and Market streets.
"She was walking down the street going to her destination with her earphones in, so there was no interaction, nothing led up to this event," said Cpt. Robert McKeever of the Philadelphia Police Department Southwest Detectives Division, which is investigating the crime.
"They were walking towards her," said Colon of the story Diana told her. "She said that they stopped and then they threw the acid."
Investigators provided Action News with photos and video of the three suspects walking away. Police say they boarded the El at 52nd Street. All three were juveniles.
"In my opinion, they were anywhere from 8-12 years old," said McKeever.
Police are working to identify the kids who were also seen on the train platform before the attack.
"They were walking around with a cup," said Colon.
Investigators are testing to find out what the chemical was.
"That would be part of the investigation, where they got it at, why they had it," said McKeever.
The chemical was strong enough to leave a mark at 51st and Ludlow and leave the victim with second and third-degree burns to her face, legs, arms, neck and torso.
The victim, 25-year-old Diana, is a transgender woman. When she was attacked, she was headed to meet friends and go celebrate the first day of Pride Month.
"We really strongly believe this was a hate crime," said Colon.
Police say the attack may have been random, but they're investigating all of the possibilities.
Meanwhile, Diana has the support of her friends and the community on her long road to recovery.
"I think she's going to come out of this stronger," said Colon, "and I'm very, very proud of her."
Investigators are monitoring social media and even going to the School District of Philadelphia to identify the suspects. Police are asking anyone with information to call their tipline at 215-686-TIPS.
Meantime, Diana's friends have started an online fundraiser that quickly grew with support from those wanting to help Diana recover.