Obviously no where near the chapters we are on now as of the moment I wrote this. My money is near the end of the series. This series does so well, I doubt they will stop it after Souma's first year. So we will likely have to wait until the graduation ceremony and then she figures it out.
The exact scenario I picture is at the graduation ceremony. She might start to get her suspicions or start to see Jouichiro in Souma before then, but I have to place my bet on the graduation ceremony. I doubt he would show up as a guest lecturer or as a special judge, although it would be funny