Fans have recently seen the actress's character Jac Naylor come face-to-face with her mother Paula, who abandoned her at the age of 12.
Speaking on This Morning today, the star confessed to experiencing difficulty with one highly-charged scene showing Jac break down in tears while confronting Paula about how being deserted affected her.
Marcel explained: "I used to find [crying scenes] quite easy but I actually found that particular scene really, really difficult. We'd spent the whole week doing really emotional stuff and then I completely blanked on the day.
"The poor director - the lovely Rob Evans - left me to myself for about ten minutes and I just couldn't do it. I couldn't get the tears to come at all.
"Eventually I started to listen to a bit of Kate Bush and I started to think about my dog dying and my husband and things like that. Eventually I managed to get it going. There's one particular [Kate Bush] song - it was my granddad's song and he died so I was thinking about that. But it took about four or five takes."
The 32-year-old confirmed that she is "really proud" of the plotline and was grateful for the opportunity to show a different side of her character.