Sunday, whose dad is Kidman's ex-husband Keith Urban, has already modelled for huge names including Miu Miu, Calvin Klein and Christian Dior.
But in an interview with Entertainment Tonight, Kidman admitted she had qualms about letting her daughter, now 18, model - until she got her mum's opinion.
"As a mother, I'm just, like, 'Okay.' My mother let me do my passion that I wanted when I was 14. Actually, before my mumma passed, she was there and I said, 'Oh, should I let her? She wants to model.'"
Janelle Ann Kidman then replied: "Well, you did it."
"I went, 'okay'. That was sort of my mumma's parting gift to Sunny was [that] she encouraged me to let her be able to follow her bliss and follow her passion and what she wanted. That's exactly what she said, 'You, kind of, have to let her because I let you.'"
Kidman's mother died in September 2024.
The star has been doing the promo rounds for the new season of her TV show Lioness, in which she stars alongside Zoe Saldana.
Kidman, who is also mum to 15-year-old Faith, said she returned to Nashville as soon as filming finished.
"I go home to my family. I've got one child in junior year and one who's a freshman.
"So, I was like, 'Okay, I got to be there taking care,' you know? Multitasking, right?"
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