The two girls are still on bad terms following their problems earlier in the series, but Scout becomes an unlikely confidante for Rhiannon this evening when she learns that the troubled student has been self-harming.
Digital Spy recently chatted to Rebecca Craven, who plays Rhiannon, to hear her thoughts on the challenging storyline.
As a newcomer to Waterloo Road for series eight, how well have you settled into the show?
"Well, obviously there's been a massive change in the show because it's moved up to Scotland from Rochdale, but I hope the viewers feel that I've settled in really well. Technically Rhiannon was in the Rochdale school although she wasn't on our screens, and she definitely came in with a bang with all of her bullying and manipulation!
"Also, off screen with all of the cast and the crew, I feel like I've slotted in and I'm really loving working up here in Glasgow."
Are you glad to play a character whose behaviour can be so extreme?
"Absolutely! It's so exciting, because she has so many different levels and layers to her. One minute she's very manipulative and evil, but the next moment she can be as charming as anything - although in those cases she's usually got a hidden agenda!
"But throughout the next ten episodes and especially in episode nine, you're going to see a massive change in Rhiannon and hopefully it's for the better."
What kind of a reaction have you had for playing the role?
"The reaction has been great as everyone has said, 'Oh, you play such an evil person!' I really like that, because it shows that I'm doing my job. If people liked Rhiannon, then my bullying obviously wasn't very convincing! Everyone has been really supportive and told me, 'Even though you're playing a very nasty character, you're playing her really well'. I can't thank people enough if they say that.
"Some reactions can be a little bit difficult sometimes, especially with all of the social networking that's about these days, where people can be a bit nasty. I just choose to ignore that, though, and if I've provoked a reaction it's great."
Why does Rhiannon have such a problem with Scout?
"It's just the fact that she seems to be everyone's favourite. Maggie and Grantly absolutely love her, plus she has the bigger bedroom! Rhiannon thought moving to the school in Scotland would be a fresh start for her and that's why she started the bullying, because nothing was going in her favour.
"Deep down, Rhiannon isn't an evil person - she's very troubled and she just wants to be loved by someone. Because she wasn't getting the attention that she wanted, she thought the bullying was the only way to get it.
"You'll also see that when people are lovely towards Rhiannon - which is shown in episodes nine and ten - she doesn't understand it because she feels that she doesn't deserve the love of a family. She's been brought up with three different foster families and they haven't exactly been the best."
What more can you tell us about tonight's episode?
"What you'll see in this episode is that Rhiannon has had enough. She's realised that everything she did in the last eight episodes was wrong, and now she's starting to take it out on herself. She has a big secret which is that she self-harms, so that is her way of releasing all of the anger and frustration that she has towards herself.
"Later, Audrey McFall catches wind that Rhiannon isn't herself, so she invites her to join a running club to help with her weight problem. Rhiannon goes along with Audrey to get her off her case, but unfortunately Scout has to come too, which is the last thing Rhiannon needs as they're not exactly friends!"
What happens next?
"The two girls go running together, but Rhiannon falls and hurts herself. Scout notices that there is blood on Rhiannon's t-shirt, and that's when she finds out about the self-harm. Scout was the last person Rhiannon wanted to know this, and she begs her not to say anything.
"Luckily by the end of the episode, you can see there's a real connection that's going to develop between Rhiannon and Scout. Everything that's happened in the previous eight episodes is put in the past, and now there's a bond that's going to grow. In the next block of episodes after Christmas, you'll see more layers to Rhiannon that you haven't seen so far, and she's been able to deal with her self-harm problem."
How did you feel about taking on the self-harm storyline?
"I was very nervous at first, because obviously it's such a serious subject. But I did quite a bit of research into why people self-harm and the different reasons for it. Some of my friends have self-harmed in the past when they were a lot younger, so I spoke to them, learned from their experiences and just tried to get as much information as I could. I wanted to make my performance as Rhiannon as truthful as possible."
Did you always know you'd get this chance to show another side to Rhiannon?
"No, I didn't! When I first got the brief for Rhiannon, it just said that she was a manipulative bully who would take a disliking to Scout. But later on, I had a chat with the producers about where they were going to take the story and I was really pleased.
"I absolutely loved playing a bully and a manipulative character, especially getting to work so closely with Katie as we're really good friends. But then to get the chance to show another side to her is great."
Did you enjoy filming so many scenes with Georgie Glen, who plays Audrey, for this episode?
"Definitely - Georgie is one of my favourite actresses on the show. She's so supportive on set and off set. Georgie has got a lot more experience than me, so we'd do rehearsals together and she'd really give me her support. She's a very professional actress, and I learned a lot from her.
"I wanted to do this storyline with as much truth and conviction as possible, and I do think those scenes with Georgie helped to bring the truth to the storyline."
Katie McGlynn, who played Scout, has now left the show. Are you missing her?
"I am indeed! I miss Katie so much. She's still one of my best friends, and I speak to her all the time now that she's gone. She's going to have a very successful career, so I think she'll be fine leaving Waterloo Road. I do miss her, because I have to put on a Northern accent for this role, so I miss having my little mentor giving me tips!"
What is your previous acting background?
"I trained in musical theatre in London, so that's what I've always done until now. I also did a film called Hunky Dory with Minnie Driver. But Waterloo Road is my big break, and doing TV is really different to musical theatre. I'm hoping the show will be a stepping stone for me to branch out into more television."
Who else have you made friends with on the Waterloo Road set?
"Definitely Shane O'Meara who plays Connor - he's the funniest guy I've ever met. Kirstie Steele who plays Imogen is great too - they're both awesome people. I've also made friends with some of the newer characters, who you'll meet after Christmas.
"We are just one big happy family, and what I love about this show is that there's no divide between the teachers and the schoolkids. Everyone supports everyone else and there's so much fun on set. There's never a dull day!"
> Read our spoiler for tonight's episode of 'Waterloo Road'
> Read more 'Waterloo Road' spoilers and news
Waterloo Road airs on Thursdays at 8pm on BBC One.