During Wednesday's "Call Me Daddy" podcast, the actress -- who played Debbie Gallagher, the younger sister to Rossum's Fiona, on the Showtime dramedy -- said there was a noticeable shift on set following Rossum's exit from the show after nine seasons.
"It was weird at first for sure, but the set became more of a positive place," the star claimed. "I remember pre her leaving, I'd go to set some days and I'd be very anxious having a scene with her because if she had a bad day, she made it a bad day for everybody."
"[Rossum's exit] was bittersweet because I had known her for so long and I have a lot of love for Emmy," she continued. "We haven't spoken in years, but that's okay. I have a lot of love for her. I hope that she finds her happiness."
Kenney went on to describe a "weird competition" between her and the actresses, which she said she never understood because there was over a 10-year age difference between the pair. "I don't know if it was other people on set creating that or if it was her creating it, but I know I wasn't creating it," said Kenney.
As for art imitating life and the pair's real-life relationship at times being a sisterly one, Kenney said "100%" it was -- "but in good and bad ways to be honest."
"We were both so young -- I was obviously a lot younger -- there were times she would try to be a good influence, and then there were times where she would be blatantly giving me ... not the best advice."
"And maybe she was struggling with her own inner problems and taking it out on other people, but we all handle situations differently," she added. "Growing up I definitely took note -- not just from her in particular-- of things I want to carry on in my life and things I don't want to carry on in my life."
After 11 seasons, "Shameless" had its series finale last April.