Dr. David Helfet was not involved in her care, but as Chief of Orthopedic Trauma at Hospital for Special Surgery, he's seen it all.
"You have to reattach the muscles, the nerves, the tendons, the skin. It's a big job and if everything mangled, it's very hard," Dr. Helfet said.
It's all too familiar for Ariel Fishman, a New Yorker and father who was also hit by a taxi last March.
"I was behind my car about to empty the trunk and drop my kids off at school when a taxi came from behind and slammed into my car crushed both of my legs below the knee," Fishman explained.
He lost both his legs.
"I remember thinking I was thankful I was still alive and also thinking I'd be able to recover," he said.
But Ariel says the road ahead for Sian Green will not be easy for the young victim. He's had 16 surgeries.
"There's bone fragments, there's debris that has to be removed from the tissue," he said.
As the swelling goes down, prosthetics have to be continuously refitted
"Over time, and through rehabilitation and through the natural process, her limb is going to get smaller," Chris Kort, President and founder of Prosthetics in Motion, said.
The months of physical therapy are grueling
"There's only so much the doctors can do, the therapists can do. Physical therapy is every day," Fisherman said.
Six months ago Ariel developed a stress fracture, which meant another setback and more surgery. But he will not give up and still plans to run another marathon one day.
He has this message for the young British tourist:
"I want her to know that she's gonna have a terrific life ahead of her. Everything she wanted to do she can still do. Everyone's gonna be cheering her on. She should know that," he said.
After his accident, he said people wanted to help in some way. If you want to do help, he says the best thing you can do is donate blood. He needed over 70 units after he was hit by a taxi.