Five years after her win at the Moss Vale Pro-Am, de Roey's round of one-under 69 and nine-under total was enough to clinch victory by a stroke from England's Cara Gainer (68).
Teenaged Thai phenomenon Cholcheva Wongras (70) snared third with Sarah Kemp (74) the leading Australian in a tie for fourth.
De Roey, 33, clinched the title on the final hole when she hit a gap wedge to eight feet and drained the birdie putt.
"I like to look at the leaderboards. I want to know what I have to do," she said.
"I asked on 15 what the leaderboard was and then on 18 before my putt I also checked.
"It was downhill, down-grain so I wanted to know that I had to just tap it there or make it."
Trailing Kemp (75) by two strokes at the start of the final round, de Roey bounced back from two early bogeys to play the steadiest hand down the stretch.
Kemp's tie for fourth was beyond her wildest expectations given the compound fracture she suffered to her right leg just seven months ago.
"Honestly, the goal was just to see if I could make the cut so it's exceeded all of my non-expectations," said the Australian, who will back up for next week's Women's NSW Open at Wollongong Golf Club.
"I'd already won this week. I was able to finish the tournament and I proved clearly I can still play golf and that's the two main objectives.
"It makes me feel really good now going back into the States."
Australian LPGA Tour star Grace Kim finished strongly with a 67 to claim a share of sixth spot.Â
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