Flushing now could perhaps be considered overwatering but I don't think it will hurt the plant in any way.
When I had brown spots and dying leaves on my first two plants, the flush helped but it took a while for them to look healthy again. No problems since. Except for the eventual mold. :/
So yeah, I would flush, then give a mild feeding and calmag with the next watering. Since she looks so perky she probably hasn't been seriously overwatered recently.
Best of luck! :Sharing One:
Hmm... I first grew in 11 liter square pots and I always gave 2-3 liters. That way I had some run-off. I ran into problems, though if I used less. So I'd advice at least 3 liters to be on the safe side.
Hmm... Looks to me like she's just starting to show more sativa characteristics. I've seen plants that start off with fat leaves like the ones you see on indica strains and grow those long, thin sativa leaves towards the end. Nothing to be worried about, I'm sure. I actually remember reading a thread where some experienced growers seemed to associate thinner leaflets with stronger effects.
You might want to give the infirmary a go with troubleshooting in general. Or just make a thread on a more frequently read section. Maybe a journal on the new grower's forum?