This is Minjee Lee's fifth career LGPA victory.
Chella Choi finished with seven birdies and no bogeys.
Liu, who shared the overnight lead with world number one Park Sung-hyun, was four-under over her last four holes.
The pioneering tournament is the only one in the world with male and female fields, playing in alternate groups on the same course and for equal prize money.
On 13-under-par, Pornanong led by one from English home favourite Georgia Hall, with South Korea's Ryu So-yeon a further shot back on 11-under.