Carla is sexually assaulted by fiancé Frank Foster (Andrew Lancel) next week after she ends their relationship on the eve of their wedding.
As confirmed earlier this week, the actual rape is not shown on screen but subsequent scenes see Frank run off into the night, while a traumatised Carla phones Maria for help.
Smith told This Morning today: "Maria just instantly is round there and completely understands - and just can't believe, actually, that this has happened. Because Carla's such a strong woman as well, it's the last person that you would think that would happen to."
She continued: "Carla rings Maria straight away after the attack. Maria runs round to the flat and instantly is like, 'Frank's done this, hasn't he?' Carla is in bits on the floor and clearly in trauma. She's covered in bruises and just distraught. Maria just says, 'We've got to ring the police straight away - because you can't waste time'."
Smith also praised Alison King, who plays Carla, for the commitment she has given to the hard-hitting storyline.
"She really did her research," the actress said. "She's done amazing - she's just been brilliant throughout the whole storyline."
Frank previously tried to rape Maria earlier this year, but the matter was not pursued by the police due to lack of evidence.
Coronation Street's dark Frank and Carla plot begins on Monday at 7.30pm on ITV1.
> Read our interview with Andrew Lancel about the storyline
> Coronation Street's dark Carla and Frank storyline: Pictures
> Read more Coronation Street spoilers and news
Watch a video preview of tonight's Coronation Street episode below: