Ashley Greene's first movie as a new mom was "challenging" when she returned to work just six months after giving birth

She told Us weekly: "This [movie] was tough for me because it was my first movie post having my little girl, and I think we were six months in, and so I'd been on set for the longest that I'd ever been on set.

"I was breast-feeding, and so I was pumping on set and your hormones are going everywhere. And then I was, like, having to go home to this little angel and try to separate these two things. It really was challenging for me."

Ashley plays a mother named Cynthia in the film and she used her own off-camera struggles to inform her portrayal.

She added: "Thankfully, I think, with Cynthia, you can always find stuff that you can use to your advantage also vs. letting it work against you.

"And so I said: 'This is really hard for me, but I'm gonna find a way through it and I'm gonna use this, these moments when I'm on set.'

'It's one of the things I'm most proud of coming out of this project."

Ashley previously opened up about getting back to her exercise regime after giving birth - insisting she wanted to make sure she gave herself enough rest and didn't work out too hard.

She told PEOPLE: "I really wanted to focus on making sure that I gave myself enough rest for everything to go back into place, and made sure that I wasn't trying to jump back into where I was and hurting myself.

"I feel like there's this idea that you are cleared after eight weeks and you can just jump back in, and that is so far from the case. I think it's really damaging to a lot of people."

Ashley works out five times a week and thinks it's good for her mental health. She shared: "My workout also depends on my baby. My life is her life now. "Physically, we all want to look good, but I want to feel good - and mentally, I have to. It's just a really empowering thing as a woman."