Can you give some extra info?like soil type,what kind of nutrients do you use and what are the ph and ec levels of your feedings,do you measure your run of?
I had a similar problem a few years back and the problem was that I used cocoblocks butt I forgot to wash it out properly before I used it the first time so I ended up with a ph problems due to salt build up from the production proces of making the cocoblock in the factory,
I always try to save a plant,if it works you learned allot more then when you just throw it out and start over,and if she rebounds @ this stage she will do just fine and will be able to yield the same as the other plants if you can give her a few weeks of extra growing time