I think you misunderstood what she said. Here's the best translation I could do.
Sugimoto: I was slim and small chested at the time. I admired/looked up to the glamorous type female body.
Sawayama: Me too, since I got into gravure work I became more aware/conscious about getting more full/plump.
Sugimoto: As I was constantly thinking about the glamorous body type, my breast just got bigger.
Sawayama: You just think and got it? (laughter)
Who know if she really has fake breast, but at least in this conversation she didn't admit or imply that she has fake breast.