The "Underworld" star was hesitant about being away from her house in Los Angeles for so long, because she was used to only taking on jobs close to home while she raised her daughter, Lily Mo - her 20-year-old child with her ex-boyfriend Michael Sheen.
However, she received the call for "The Widow" just a day after Lily left home to settle into college life in New York City, and Kate realised she no longer had an excuse to turn down challenging gigs.
"I'd been saying, 'Oh, I've stayed home a lot because (of) my daughter, and then my daughter left, and one day later, they (producers) said, 'Do you want to go to Africa for six months?'" she recalled.
"And I was like, 'No, I don't, I'm too scared!'" Kate continued. "But then I had to, because I'd been saying (I was staying home for my daughter)..."
The British beauty ended up enjoying her time abroad, because it gave her an opportunity to travel somewhere new: "It's great, and I probably wouldn't have spent six months in Africa (without the show)," she smiled to U.S. breakfast show "Live with Kelly and Ryan".
One thing Kate wasn't quite prepared for was the chilly temperatures in South Africa, because she thought it would be warm and sunny all year round.
"They have winter in South Africa, which no one told me...!" she exclaimed. "Because we were there six months, we ended it wearing thermal underpants and a big jacket (during the winter months), and I never see a picture of a South African person standing next to an elephant with like, a muffler (scarf) on. They keep that really quiet, so it was shocking!"
The cold weather was a complete contrast to the scorching hot summer months the cast and crew had endured during the start of production, which caused some of them to seek medical help in hospital.
"It's very hot (during the summer), and I actually keeled over from being too hot...," she shared. "I wasn't the only person who keeled over, it was a few of us (who) dropped...!"
"The Widow", in which Kate plays a woman searching for the truth about her past, premiered on streaming service Amazon earlier this month.