"It's easy, like changing into second gear," she says.
With season three of the hit Australian family drama series currently screening in New Zealand and season-four filming almost complete, Marais admits slipping into character has almost become "automatic".
"People assume that we are similar, but there is a division," notes the 26-year-old, South African-born, Perth-raised graduate of the National Institute of Dramatic Art.
One of the similarities is that Marais' love life has imitated her art.
In October, she and James Stewart ( 34), who plays her on-screen love interest Jake Barton, became engaged after an 18-month romance that began after they met at his Rafters audition.
Apparently, the chemistry between them could not be ignored.
On and off-screen romance aside, red-carpet regular Marais says fans who recognise her in the street sometimes do expect her to be like glamorous Rachel and are often surprised (or disappointed) when they see her out in track pants and ugg boots - and will say so.
"It's weird that people think they know you because they see you in their lounge room [on TV] and they feel that they have an instant relationship with you.
"Sometimes they think that they can ask you very personal questions which no-one else would ever ask.
"But I try not to let that worry me, because it's lovely that people are so supportive of the show.
"It is hard.
"There is a lot of pressure, plus the pressure any normal 26-year-old would have in life and you're living it out in the public eye," Marais says.
"But it has all been worthwhile."
- Packed To The Rafters screens on Wednesdays at 8.30pm on TV One.
