There is definitely a problem if you are using a 400watter and she is that small after four weeks.(Assuming the pic isn't making her look small, can you measure her?) Grown under ideal conditions a plant should be close to a foot by four weeks. What strain is she? If you are watering her properly and she's wilting I'm going to say that there is some kind of root problem. Is she getting fresh air to her roots? Does the pot have proper drainage?