"Our makeup artist, Morna Ferguson, was amazing with me on the film," Ronan, 21, tells PEOPLE. "I always tell her this even though she won't want to hear it: If it wasn't for her I would've been even more of a basket case than I already was."
The 1950s-set film revolves around idealistic yet practical Irish immigrant Eilis Lacey (Ronan), who finds herself swept into a new life of romance and a difficult decision between allegiances to her home countries, old and new.
Ronan says making the film was emotionally draining due to her personal connection to the material and having also moved away from her native Ireland.
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"I was very emotional because it was my mom and dad's story," Ronan recalls. "They had moved over to New York in the eighties and I moved over to London about eight months before we started the film and I was experiencing homesickness."
The Irish actress says Ferguson kept her from letting the swirling emotions overwhelm her.
"To go into a film that was that personal about home, there were times when it was really overwhelming," she says. "And it was Morna being there, being the voice of reason, very much being the mommy to everyone on set. She was the one who kept us all calm. She was really wonderful on Brooklyn."
Ronan also talked about other women who inspire her, pointing to fellow Oscar nominee Cate Blanchett as one of her acting role models.
"I worked with her briefly [on 2011's Hanna]," says Ronan. "She's one of the greatest actresses of our time and you can tell to her core she's an actress. It's all about the work for her. I think it has a lot to do with she took a break from film to become the artistic director of the Sydney Theater, and I find that very admirable. That somebody – when they're at a certain point they're probably being offered everything under the sun – can actually just turn around and say no and step away from all of that."
In addition to Blanchett, Ronan cites her Stockholm, Pennsylvania director Nikole Beckwith as a key influence on her artistic taste.
"This word gets thrown around a lot, but she is a brilliant filmmaker and she is a true feminist," says Ronan. "Working with her right before I did Brooklyn, she was really influential in how I think about film and how you can use your role to say what you want to say. She is somebody, especially for a female director, who is so secure in who she is, she'll never really waver from that at all and she'll fight for exactly the film she wants to make, which is what she did with Stockholm, Pennsylvania. She really inspired me an awful lot as well."
Ronan adds that Beckwith made her interested in examining the way women relate to one another.
"I want to explore female relationships more," she explains. "That was so great going on to Brooklyn because there are so many scenes where it's just one woman being kind to another and helping another woman. It was lovely to have that all happen around the same time."