The 27-year-old Prammanasudh had five birdies and sealed her second LPGA Tour title by two-putting for par from 20 feet on No. 18 to finish at 14-under 202.
Lee closed with a bogey-free 68.
Prammanasudh was sharp and steady all day, never allowing anyone to catch her. The former University of Tulsa star also won the Franklin American Mortgage Championship in 2005, the last tournament she led heading into the final round before this week.
After holing her final putt, a 2-footer for par, she shook her arms in the air and kissed her husband, who also is her caddie.
Rookie Angela Park (71), making her second LPGA Tour start as a pro, Japanese star Ai Miyazato (66) and 18-year-old Morgan Pressel (69) tied for third at 11 under.
Park and Pressel, who finished fourth at the season-opening SBS Open, are both 18 and were vying to supplant Paula Creamer as the youngest winner of a full LPGA Tour event.
With a three-hour rain delay Friday, 70 players had to return to the course Saturday morning to complete the second round.
Prammanasudh took sole possession of the lead early, sinking short birdie putts on the first two holes to take a two-shot lead. She missed the green and bogeyed the par-4 third, but hit an aggressive second shot over the water on the par-5 fifth that set up a two-putt birdie from 30 feet to get back to 12 under.
Park and Lee also birdied the hole to stay a stroke behind Prammanasudh.
Prammanasudh parred the next five holes before holing a 5-foot birdie putt on the par-4 11th hole.
After missing a long eagle putt, Prammanasudh tapped in for birdie with her belly putter on the par-5 13th to reach 14 under. Lee stayed a stroke behind with a birdie.
Lee had a chance to tie Prammanasudh on No. 17, but missed an 7-foot downhill birdie putt. Lee had a chance to force a playoff, but missed a 50-foot birdie putt on 18.
Park was tied with Prammanasudh for the lead heading into the final round at 10 under after playing nine of her second-round holes earlier in the day. But she couldn't make a move, missing several birdie attempts.
Cristie Kerr, assessed a two-stroke penalty in the opening round, closed with a 65 to tie for sixth with Vicki Goetze-Ackerman at 10 under. Mi Hyun Kim (69) was another stroke back along with Wendy Doolan (70).
Creamer (67), who won the SBS last week for her third LPGA Tour title, was 7 under along with Aram Cho (70), Michele Redman (70) and Nicole Castrale (71).