But she admitted that very few of her friends and family knew she was planning on becoming a mother.
She said in the interview: "I can count on one hand the number of people who knew that I was having her. But she is the biggest blessing I could ever imagine. It's the best thing I've ever done."
She went on to insist that she still loves modelling, but admitted that it gets more "nerve-wracking" as she gets older.
"I still enjoy it but it's nerve-wracking ... Because I'm 51 years old walking with girls who are 18! It's great to be with these young 'uns at my age, but I have to say, at one of the shows I was like, 'Come on, girls! Pick up your feet! Why are you walking so slow?'"
She added: "I definitely feel like my time was more joyful. We smiled! We got to show off our personalities."
On becoming known as a figurehead for a younger generation of black models, Campbell said: "There were lots of times when I would walk in the fashion shows, but I was never picked for the ad campaigns and it would hurt – it really hurt.
"I would have to suck it up and keep moving. Of course, it would have been great to have had that support around me back then, but I'm proud to see it happen now, I'm proud to see the diversity now."
Campbell first revealed that she had become a mother nine months ago.
She surprised her Instagram followers at the time when she shared a photo of herself cradling her baby daughter, writing that she had never felt a "greater love".
Alongside the first look at her newborn baby, whose name has still not been revealed, Campbell wrote: "A beautiful little blessing has chosen me to be her mother.
"So honoured to have this gentle soul in my life there are no words to describe the lifelong bond that I now share with you my angel. There is no greater love."