Merna, whose character Carmel McQueen is currently struggling to come to terms with disfiguring facial burns, told The Mirror that 26-year-old Piper is "an inspiration".
© Ian West/PA Wire/Press Association Images
© PA Images / Ian West/PA Wire
"Katie is a beautiful girl," said the 28-year-old actress. "What happened to her was horrific. She is such an inspiration, the work she does for charity is incredible."
Piper was left scarred for life after an ex-boyfriend arranged an attack in which acid was thrown in her face. The former TV presenter was blinded in one eye and has undergone countless operations and hours of therapy in order to rebuild her features and regain facial movement.
Merna described preparing for scenes where a tanning lamp exploded in her character's face as "heartbreaking".
"In Hollyoaks, Carmel is this beautiful girl and something horrific happens to her," she said.
"For Carmel it is heartbreaking because she is all about how she looks. She can't cope with her injuries."
© Lime Pictures
In her despair, the character contemplated suicide and had to be talked out of jumping off a building by a friend.
"It's very scary that people get to the point where they can't talk to anybody," Merna continued.
"I have had some amazing messages on Twitter from people saying that it's helped them. Sometimes Hollyoaks is all about comedy, so it's great to get something gritty and meaningful like this."
© Rex Features / Steve Meddle
Merna is also involved in a campaign that seeks to highlight the dangers of sunbeds and supports the push to raise the legal usage age to 18.
"I want to say to people out there, be very, very careful when it comes to electrical tanning," she said.
"I can't tell you how important it is to me to get that message across, especially to young girls. If you put your face in front of an electrical device, these situations can happen."
She added: "Because of peer pressure to look brown I started using sunbeds when I was 15 and I used to burn.
"I had a photo done a few years ago to see how much sun damage I had and it was really shocking. You don't realise how much damage these things do to you. Sunbeds are the main cause of skin cancer. Young girls shouldn't be under any pressure to tan."
