In the show, which tells the story of a teenage boy in Sheffield who wants to be a drag queen, Miss Hedge is the main antagonist, out to quash poor Jamie's showbiz dreams.
"I am not cold," Hayley says, confirming what a leap the character is for her.
"I am huggy and warm and want to cuddle everybody – whereas she's just a bit over life."
In fact, Hayley has already played Miss Hedge before, in the West End production of Jamie back in 2019 – and it's proving a joyful return to the role.
"Even though I'm a few years older, I've apparently still got the moves," Hayley laughs, when we catch-up in a break from rehearsals.
"I'm dancing around on tables – and I get to rap, which brings out that inner Vanilla Ice in me."
As Hayley explains, for her Miss Hedge is not a villain but someone who has simply been beaten down by disappointment – and has more in common with Jamie than it might seem.
"The way I see her, she's a really frustrated club singer. And that's all she wanted to do, but she couldn"t because there was no money, and she ended up going into teaching to make a living.
"And she looks at Jamie as this kid she kind of sees herself in a little bit, but she can't let that side out."
Miss Hedge also reminds Hayley of teachers she encountered as a young kid growing up in Blackpool who was desperate to perform.
"I did have one teacher, Mrs Crossley, who was ace – she used to tell me "be whatever you want to be, go dance, go sing".
"But a lot of teachers said 'you'll never make it Hayley, it's too difficult, don't try and do it' – and that just made me want to do it even more."
Indeed, from baby ballet classes onwards, Hayley never looked back – after graduating from drama school, she went straight into a West End musical, before aged 26, landing a role that would change everything for her, as the lead in a Sheffield revival of A Chorus Line.
Amid the audience for that show was Emmerdale's casting director – and so it was that she landed the part of the irrepressible Del Dingle.
Alongside her successful telly career, Hayley has continued to tread the boards, appearing in the likes of Chicago and Thoroughly Modern Millie.
What she says is particularly special about Jamie, however, is the sheer passion of its fans.
"It has the biggest fanbase that I have ever known in any show. They hold parties for the cast, and they are very prominent on social media, so if anybody in our company was getting grilled by anybody, that fanbase would step in. So we're very lucky to have that."
And Hayley can't wait for the show to now pick up new fans all around the UK – particularly because of the powerful statements it makes about tolerance and self-expression.
"The more towns we can get this show into, the more parents are educated, the more kids that watch and go 'I did bully that other kid at school, I should stop that' – the more we can get the word out there, the better."
Everybody's Talking About Jamie visits Theatre Royal Brighton until Saturday 11th November 2023. CLICK HERE for tickets.