Were them from seed or cuttings? Each seed has its own characteristics and tendency, if theyre different strains, she could be ready before the others, same goes for is theyre from seeds.
If theyre all from a mother plant and were put on 12/12 together then its more likely nute deficiency if you dont think shes ready, or if shes on watwr alone towards the end this will happen. Message if you need futher assistance