She closed with a final round 7-under 65 to finish on 20-under, two shots ahead of South Korea's Mirim Lee.
She celebrated the win with her 15-month old son.
"I could just tell by everybody's reaction that I had won," the 37-year-old told Yahoo Sports
"It was just amazing having him there, and he just gave me a big smile and a squeak. He's screaming now. That's his thing, and I always hoped this day would come. And now it has. Just so proud.
"I love to win. Golf has always been great to me, always given me special moments like this. I've been working with a new coach, and I definitely found something this week. He said I was going to have a hot round, and he was right. I just found something. I'm just real happy right now."
"I just found something," Kerr said. "I'm really happy right now."
A tearful Kerr had vowed to win after her caddie, Greg Johnston, mourned the death of his father last week.
"I played for both of us this week," she said. "I said I was going to do it and I did it. Golf has always given me special moments like this and I'm grateful for it."