"It was hard work," Holmes, 37, told PEOPLE at the film's world premiere at Tribeca Film Festival in New York City on Friday night. "But, I had a great team around me that really helped."
This was the right time to pursue directing, she said, because she finally felt she was ready to do it and jumped at the opportunity before she could talk herself out of it.
"It happened rather quickly. I found the book and I had the support of my agency and then Jane [Rosenthal] decided to produce it," Holmes said.
Watching Holmes handle both acting and directing in the same movie impressed her cast members.
"It was like Clark Kent to Superwoman or Wonder Woman back and forth. She would literally run from the scene, run around and look at it and make it was good. But, every time, she'd ask, you good with that?' " said Mark Consuelos, who stars in the movie as a real estate agent and love interest for Holmes' character.
"I was really, really impressed," he added. "To be in control or have all the answers everyone wants and also star in the film is an amazing feat. It's a daunting feat, and I think she did a wonderful job."
Stefania Owen, who plays Holmes' daughter, says she knows juggling both roles couldn't have been easy, but Holmes made it look like a piece of cake. "The way she did it was so light-hearted," Owen added.
"She is definitely one of my role models," the 18-year-old Carrie Diaries alum said, adding that Holmes inspired her to pursue directing. "Katie said that she wants to be in the movie I direct. So, we'll switch roles soon."
Adapted from Annie Weatherwax's 2014 novel, All We Had follows Rita Carmichael (Holmes), a single mom, and her daughter Ruthie (Owen) as they teeter on the edge of poverty during the mid-2000s.