Nute burn

Ya that lady is looking pretty full of nutrients for this far along in flower, I think you're ok reducing, then going to plain phed water till the end at this point. You can tell she's getting close and trying to drop some of those lower leaves already. All the cool colors will come out at she fades now.

I m no pro with soil but flush with plain ph water and leave for a good day or 2 would be my call. As for flush in soil it’s normally a 2 week flush so if your flower is a 8 week then yeh just straight flush from now will be fine.