Google osmosis and turgor. You will find your answer there.Over and under watering are determined by stem and leaf posture.
Your overwatering cause your stems are erect, if the stems droop with leaves, your underwatering.
My first impression after seeing the pic-----not enough light----use at least a T5.Over /under watering. Or nute deficiency ??? She got fungus nats which I'm dealing with but she's slow growing and now leaves are limp