I'm not sure myself, but for purposes of defining this, Larson's win has usually been credited as the single-day record by a single person on a network daytime game show.
So that nixes any syndicated offerings, including Hunt & Tune, and couple's efforts on Dream House are out (which for THAT category, wouldn't they be a show onto themselves?). And even with the episode split of Larson's run, they defined a single game as one day. It's no one's fault that the game took as long as it did.
With the definition properly narrowed like that, I would say that it would probably be either some double showcase winner and beyond on Price, or if a mega jackpot was won by a first-time champ on Password Plus late in the Kennedy run. (What WAS their highest progressive win, anyway?)