If its the same strain in the same nutes, then the droop is probably caused by something above the corex? I just had a gander at your last pic, and I think your droopy girl might have too much airflow over her, could be causing her to evaporate off quicker than she can drink. She does look a bit darker than righty (who looks pretty bloody good btw!), which could of been caused by her drinking up more and therefore taking up more N, causing a bit of nitrogen toxicity leading to stunted growth. I had a bit of N Toxicity on my first NFT grow.