Fans were shocked on Thursday night when Moira discovered Holly's dead body in bed and a foil package lying on the floor next to her. It was a particularly powerful scene as there had been no inkling beforehand that Holly would die.
Speaking to the Radio Times, Sophie said: "We wanted to highlight how hard and destructive drug addiction can be. Of course, there are many positive stories out there where people are doing really well and have recovered from drug addiction and therefore this Emmerdale storyline of course doesn't represent everyone."
"This is Holly's personal story," she added.
"Drug addiction is shocking sometimes and you can look at someone like Holly and think she has everything sorted in life, but out of nowhere everything can spiral out of control."
Sophie made her Emmerdale debut in 2009, leaving the soap three years later. She returned in March this year and although fans knew she had quit the show, there had been no inkling her character would be killed off.
"I always knew I was only coming back for a six-month storyline and I knew it was going to be drug-related and heartbreaking," she said.
"I was prepared for this and I knew what I was signing up for when I spoke to the producer about returning. The Emmerdale script and story team had already planned Holly's return and what would happen to her, so they really wanted me on board to help tell this story."
Sophie added to our colleagues at Digital Spy: "It's been challenging to highlight drug addiction and it's a very serious and stark warning to show the devastating effects it can have on people. Holly was a normal girl from a normal family, who went down the road of drug taking and drug abuse.
"It wasn't because of bad parenting, or neglect, or lack of education. She was a girl who made a bad decision and that decision could have been made by anybody. She has an addictive personality and it spiralled out of control - and we've really seen that whole storyline play out with her recovery and relapse."
Meanwhile, Sophie's onscreen step dad Jeff Hordley appeared on ITV's Loose Women today to discuss the harrowing storyline and what comes next for the family.
He said Sophie had been "alright" about the storyline, saying: "When one of your team goes, we were all gutted. I think Sophie wasn't ever going to stay for too long anyway as she's young, she's a great actress and she wanted to do other things. She was alright about the storyline and wanted to service it properly."
Jeff also praised the Emmerdale team for keeping the storyline secret, saying: "I think it's good we did that because nowadays there is too much feeding through media or social media."
He added of his own character, Cain Dingle: "There is a lot of guilt on his part as he was always pushing her, I think to shock her out of it, saying, 'Once a druggy, always a druggy' and it really backfired in his face and now she's gone. He has to live with that guilt and Moira has the loss of her daughter."
"Addiction is a really important theme to show on television and the way we've done it is really well done."