The two actresses play unlikely partners in the film, based in the 1840s, and Kate admits it was wonderful mapping out the love story with the "Little Women" star.
"It was interesting for me, shooting the more intimate scenes with Saoirse," she tells WENN. "We totally adored each other... and being allowed to adore each other was just brilliant. It was really empowering, playing those two roles together - more than I've ever felt empowered before."
"It made me almost annoyed with myself, in the sense that I've filmed intimate scenes before, but mostly with male actors - and it suddenly occurred to me that there is an automatic power dynamic that comes into play when doing that type of scene with a man. As a woman, you assume the man will take the reins, or steer the energy of the scene, and you as the female character will be 'taken' in some way."
"I realised that I have allowed myself to be that taken one. It's been absolutely fine, I've been perfectly comfortable with it, but to be in a situation with Saoirse, where it was utterly equal, it made me feel kind of angry at how that hasn't occurred to me before."
"Why shouldn't I have felt equal to my male counterparts...? We have to make a noise about wanting to be equal, about deserving to be equal."
Winslet, now 45, adds, "Now more than ever, I do feel telling these stories, where you see women breaking away from societal norms, it's incredibly, incredibly important. I feel very lucky to be part of a movement just now; and filmmaking is a crucial part of that movement, keeping female voices loud and proud, sharing these stories and telling them in a truthful, sincere, emotional way."
"A lot came up for me - lots of really interesting new things about being a woman. I've always felt as though I stand on my own two feet, and have a strong voice, and I'm quite proud of that - but I've only just begun."
And Ronan, 26, felt just as blessed working with Kate, revealing she was the ultimate professional, while being "kind and lovely to everyone."
"She's also willing to do everything for the job," the Irish actress explains. "She's willing to look as ridiculous as possible in order to get a certain shot, or be cold and wet in the rain for as long as it takes to get a good take. It doesn't matter to her. She's so committed to what she's doing and she's got such a great sense of humour about the whole thing. She's just got a really great attitude about work."
"I've just absolutely loved working with her. I'd never done a sex scene that was so intense and full-on before. But to be able to do that with her, I did feel very, very safe, like we could go anywhere with it and still be kept safe."