What's up duck?

Flush will cure nutrient lock out PH issues and remove excess nutrient resetting the grow medium so you know what she has on her plate for dinner

Flush followed buy proper feed and start letting woukd dry out between watering

hi growmate..!!💪 it's just overwatering, dont worry .. you can take the yellow leaves off and keep watering with nutrients!!! Be carefull, enjoy and good luck!!!!

If you fed her as bigger sisters and watered while she was still heavy - you created yourself build ups with excessive food and now those salts causing lockouts. In less terrible scenario she overgrew pot and small mistakes in watering causing first root rot signs. Transplantation maybe ? All the best !

I think @ezzjaybrush is right, Could also be getting locked out by to much of some other nutrient or PH. As your growing in Coir, if its not buffered it will rob the nutrient solution of calcium and magnesium. May just need a supplement of calmg for a bit. Good Luck

Given that you have 3 others that look great- I’d really rack your brain for what difference that one has had.. It kinda looks like potassium deficiency, as when it’s low on potassium- internal temps of foliage to climb and causes protein cells to burn and degrade. That’s what it looks like to me. Possibly could be magnesium deficiency, but I’d bet potassium first. Hope this helps amigo