The 24-year-old is placed third heading into the final round.
The 24-year-old is tied for fourth place, after a strong second round.
In her last pre-Olympics hit-out, the Kiwi is just off the leading pair in France.
The 24-year-old began the day a stroke behind the leader.
The 2010 champion is in pole position for another crown, sitting at 12-under.
Fox is seven shots back of leader Oosthuizen, tied for 17th after his second round.
Elsewhere, fellow Kiwi Daniel Hillier is tied for 91st after a two-over first round.
"It makes it feel like home having a familiar face there to play with."
Danny Lee posted an X-Ray on his Instagram page.