The 29-year-old heads into day four 11 under par, with Anne-Lise Caudal, Carlota Ciganda and Stacey Keating in hot pursuit.
Luna told the Ladies European Tour website: "I've lost play-offs twice here in France and haven't yet lifted the cup, but there are no Johnsons on the leader board today [Saturday] so hopefully this year is my chance!
"I hit 16 greens in regulation today [Saturday] so I've been playing very good."
Luna went four shots ahead after making three birdies in a row from the third and extended her lead thanks to a birdie on the seventh and was six clear after Keating bogeyed 11 and 12.
Luna herself bogeyed at the 14th and the last, but Keating also dropped a shot on the 18th.
Caudal is also eight under after a third-round 67. After bogeying the first she made four consecutive birdies from the fourth and, although she dropped two shots in the middle of the round, recovered with an eagle on 15.
Like Caudal, Ciganda began with a bogey, but picked up four shots at the third, sixth, 15th and 17th for a round of three-under 67.