The former Casualty star admits doctors, lawyers and other professional roles are her more usual screen appearances.
So she knew she had to show she could really look the part as larger-than-life cleaner Maxine in the popular Kay Mellor-penned drama.
“I could see in my mind just what she needed to look like,” Sandra told iN10.
“She’s a full-on leopard print coat, blue eye shadow type of girl. She likes to stand out.
“So I got myself that kind of an outfit for the taped audition and then got it all on again when I went to meet Kay for the next one.
“Normally you’d do a little nod to the character with your hair or whatever, but I decided I really had to go all out as I really wanted to nail this.
“It was such a different look for me. I generally wear jeans, not a lot of make-up, don’t do much with my hair and am a bit scruffy, really.
“So I really enjoyed getting Maxine’s sort of bold glam look. It was quite liberating.”
The first series of In The Club followed six couples who had bonded in their local parent craft class and faced parenthood together.
Hermione Norris, Katherine Parkinson, Christine Bottomley, Jill Halfpenny and Tara Fitzgerald were among the cast.
Now, 10 months on, the new series both follows their fortunes and those of new characters such as Maxine and her daughter Shelly, played by Gemma Dobson.
She’s acting as a surrogate for her employers, Andrew and Nathan, who want to become parents.
“Shelly wants to do this to pay off some of her loans but Maxine’s not altogether happy.
“Shelly is headstrong and insists it will be fine and that she’ll be able to give the baby up.
“But as a mum-of-three, Maxine knows how strong that maternal bond is and how tough it will be.”
Sandra and husband Jonny have a six-year-old daughter Elsie and she says that being on a set full of babies took her back to Elsie’s earlier years.
And she admits being a mother made a big difference when it came to dealing with the babies on the show.
“I found it really helped,” said Sandra, 42.
“You just have a natural instinct for things like handling a baby. You have a confidence through having had your own.
“You’re dealing with someone else’s precious child and you obviously have to be very careful.
“For some of the younger cast it must be really terrifying.
“You’re trying to remember all your lines and what you have to do and then you have this little thing that seems like glass.”
With four months of babies as the subject matter and infants around all the time, Sandra says that the chat among the cast was of anything but when filming stopped.
Having real babies around, though, made for a very different feel to other shows Sandra has worked on.
“We had prosthetic babies for scenes where the baby wasn’t in shot.
“But then they’d shout: ‘Babies on set’ and everything changed.
“It was very calm and quiet but you knew there was a pressure to get it right. You could only have the real baby for 10 minutes at a time so you had to get it done.
“There were times they wouldn’t cry or smile or feed when you wanted them to. But I always preferred having a real baby as it’s easier when you have that little thing to react to.”
It’s already been a stellar year for British drama with The Night Manager, Undercover and Happy Valley just three of the acclaimed hits that have had everyone talking.
Mellor series, like Fat Friends and The Syndicate, are always welcome and Sandra agrees that British drama is in a good place.
“I think we’re producing some brilliant stuff at the moment and I feel very lucky to be involved,” adds Sandra.
In The Club, BBC1, Tue, 9pm.
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