The 42-year-old overtook fellow-Scot Carly Booth, who injured a knee playing in a charity football event earlier in the week.
Booth, the Aberdeen Asset Management Scottish Ladies' Open champion, had a closing 72 for three over and was joint 62nd on her debut in the event that will become the women's fifth major next year.
South Korea's Park Inbee had a superb day with the putter to win the title – a second to add to the 2008 US Women's Open. The 24-year-old started the day tied with American Stacy Lewis, but had 11 single putts and eight birdies to post a 17 under total. She won by two shots from Lewis and Karrie Webb, the veteran Australian who won in 2006.
Lewis, the leader from round one, eagled the last from 30 feet for a 68, while Webb birdied the final two holes for a 67. China's Feng Shanshan, who holed a bunker shot for an eagle at the last and a 66, South Korean amateur, Kim Hyo Joo (68), and the 2007 Champion, Natalie Gulbis (68) shared fourth place on 14 under.