Flushed for 10 hours? Probably drowned it. I've always fushed in a two week period. Flush meaning only use water and maybe add simple sugars instead of nutes in that two week period.
Can you just rub it off with your finger? If not, probably not mildew or mold. The plant is not old enough for notes in my opinion. Wait til she is 8 or 10 inches tall/about 2 or 3 more weeks if she isn't that tall by then. Should be fine.
If this was a western, they just got the cowboy from underneath the bull and realized his chest is crushed. The cowboy knows they can't save him. Your plants are the cowboy. You are the bull. Try and harvest it now. Make rso, shatter and or cannabutter ext.