Should I defoliate?

Ask the person who advised you ... It could be either salt build up around main stem area because you watered that place most or even only, then you needed to prepare like 50-60 liters room temperature, right ph water and go it all through, with last two liters it should be some calmag and very light percentage of feed, i personally never made it right and think in soil its false way of sorting, plain water, good watering regime sorts most. It can be root bound, too small pot, plus some ph issues. just good watering regime and correct/right diet would drag her okeish to the end Could be overdose and lockout ..... , plain water for 3-4 full wet/dry cycles, it should take you almost two weeks before returning to feed. Now i would just water her when pots are super light and water for sure all used. load with pk part and heavily reduced N part for few weeks and then stop all feeding, carry on with plain till harvest. check your meter, maybe he shows how milk is fat, but not ph, it happens to them very often, you have to re-calibrate and clean them monthly, plus maintain correctly ....

I’d pull off some of those little buds not getting any light like in pic 6

I tried to fix the pH again before 3 days, i flushed her repeatedly with pHed water of 6.4, but still the runoff water after many flushes was around 7.2. Next time she's dry, should i feed her the bloom stuff, or flush her again?

no. think still ph is off, or your feed doses, schedule or something - not working. When you have any issues with girl is better to leave all itchy fingers for HST type stresses for next grow. Just finish her.