Supamas Sangchan fired a final 69 to win the individual title at the 35th Queen Sirikit Cup in Taiwan yesterday.
The 17-year-old Thai made three birdies in a bogey-free round at the par-72 Sunrise Golf and Country Club to win by three strokes on 214.
Australia's Oh Su-Hyun (74), ranked fourth in the world amateur standings, came in second on 217 while Park Gyeol of South Korea (75) finished third on 218.
Benyapa Niphatsophon shared 13th place following a 80 while Ornnicha Konsunthea was tied for 15th after a 82.
However, Supamas's victory could not help Thailand win the team title. The Thais, who shared the first-round lead and were tied for second after two rounds, finished third on 439, two strokes behind champions Australia.
Japan were second on 438 while defending champions South Korea were fifth.
Thailand's best finish in the team category at the amateur event was second in 2005.
Thailand coach Virada Nirapathpongporn said she was disappointed although the team fared better than she had expected.
"Honestly, I would have taken the third place before we boarded the plane," she said.
"However, after seeing that the South Koreans were not that strong and our players performed well, to finish third was disappointing."