Reto shot rounds of 72-69-70-71 for a total of 282 – five shots behind winner Ha Na Jang of Korea.
Fellow South African Lee-Anne Pace carded rounds of 72-72-71-70 to finish in a tie for 22nd.
Reto signed off with a 71 to tie for ninth on six under alongside US trio Austin Ernst, Lexi Thompson and Alison Lee, while Pace returned a final round 70 to join PK Kongkraphan from Thailand and American Stacy Lewis on three under 285.
Jang closed out a 2-stroke victory on 11 under 277 over Brook Henderson from the US with a final round 75.
This marked a career first LPGA Tour victory for the 23-year-old Jang from Seoul, who recorded six career victories on the KLPGA in five seasons before making the jump to the LPGA in 2015.
Original source: Paula grabs first top 10 finish