"It was really hard," said Piper's younger sister Suzy. "One day ... you sort of thought, 'Oh, you know, maybe she's getting better.' And then it could be even just half an hour later ... she wouldn't speak or she would be really upset or she'd be angry. It was like a roller coaster."
For over a year, Piper only left her home for trips to the hospital. She'd done all of her shopping online until Suzy convinced her to go to the mall to buy a dress.
"It was hard. I got very low confidence, low self-esteem," Piper said.
But the outing proved to be a blow to Piper's confidence when shoppers stared.
"People [were] walking into things because they were staring at me," she recalled. "I don't think everybody was doing it to be unkind. I think some people just are really uneducated and ignorant to why I looked the way I did."
But Piper slowly began rearranging her life. "She sort of reached this conscious decision ... when she said, 'I am not going to be a victim. I'm going to be a survivor,'" David Piper said.
Eighteen months after the incident, the former self-described "party girl" decided to throw a party for those who were a part of her terrible but triumphant journey.
"I'd accepted that this was me. This was my new, beautiful face," she said. "I'd had a lot of help from the people that really mattered. I wanted to thank them in a way that I could ... and I knew it would mean a lot to those people to see me enjoying myself and out. I think that was a reward to them and to me as well."
"I just remember, just the simple things ... just getting ready together, like the two girls again," said Suzy. "Putting our makeup on, putting little dresses on and stuff. It was just so nice because that's the Kate that I knew. And like we always used to do girlie stuff together like that before."
At the "coming out" party, Piper's guests waited at the bottom of the stairs.
"I never dreamed that we'd see her like that again," said Suzy. "And so to look at her I just thought that it's Kate again. She's back, you know. And it was so nice."
Her next milestone was leaving the house alone. Piper took a short walk into town. It was an emotional moment for Piper and her mother.
"I think I've got a chance to build a life, and I don't know if it's going to be that easy, but I want to try. I don't want to be a scared little child. I want to blossom into a confident, able woman," she said. "The scars, the mask, everything encased me in this little shell, and I want to break free and be my own person ... I want to be rid of that and just be Katie."
Piper first told her story in a British television documentary, "My Beautiful Face," which gave her the platform to rebuild her life. She now wants to help other burn victims receive the same extensive rehab that she did.
"We actually talk about it now -- she wants to set up a clinic here in London so, you know, anyone who is burnt can go to this clinic for as much rehab as possible," said best friend Kay Little. "I think she's actually probably got a brighter future now than she had as a, you know, as a model and, and TV presenter."
Piper admits that, before the incident, she was self-obsessed.