For some reason, I think you have a serious iron deficiency with this one plant... she is exhibiting all the symptoms - and iron deficiency comes from your PH being above 7.0. I can't tell you why the OTHER plants are not showing this but perhaps they will start to soon.... It doesn't matter, though - you've got to get your PH under control with her and probably all your other plants. My mantra on this subject to EVERYONE is that you should invest in a PH pen as it is the single most important tool you can have for any grow. I prefer Apera as it's just as good as (but cheaper than) Blue Lab. If you don't have one, get one NOW. You can't rely on strips or drops of tester fluid in a small vial and trying to match colors to a printed chart... those are WILDLY inaccurate for weed purposes.
What you need to do here is to flush her out - that means running ph'd water through her to clear out all the nutrients and salt build ups and get her PH back into proper range (6.0-6.5). You want to run 3x the water as the pot size so if you're growing in a 3 gallon, you should run 9 gallons of ph'd water through her. In the last gallon of water, add your nutes but at 1/2 strength... and let her dry out before resuming your normal water/feed/water/feed schedule. No matter what you're giving your plants, you should always make sure the PH is in the proper range!
Good luck - I think this is easily solved and she'll be ok!