I can't really make much out of the photo since the medication was applied, but it looks like the frog is still there? Unless its that area near the bulbs, but I can't tell whether its missing or if the light is hitting it oddly.
Honestly, I wouldn't freak out too much. I'd go check and see myself and make an educated decision on what to do. If she wasn't in any pain during the lesson, she isn't in any pain now.
I use peroxide for thrush. It attacks the bacteria and dries out the hoof immediately. I've only used it 3 days in a row because of how effective it is. You don't want to over-use it because it can dry the hoof out too much. I put peroxide in a squirt bottle and use it that way. Much cheaper than Thrush Buster and much more effective.
And those who were seen dancing were thought to be insane by those who could not hear the music