I would say 2 things - 1) not enough light, and 2) soil that is too shallow.
Cannabis likes to grow a deep and wide root system, certainly deeper than the soil level in your container and by now, the roots will be hitting the base of the container, signalling to your plant to slow down. A good soil depth is 30-40cm. Also, by having the seedling so deep down in the container, if growing outdoors, it will only get light when the sun is high in the sky, say 10AM until 2PM and this is not enough. If growing indoors under artificial light, it again only receives overhead light and misses out on all the reflected side light that "bounces" off the walls of the tent/room, again reducing growth by just not getting enough light to stimulate adequate photosynthesis.
As BioBuds said, watering when the top 2-3cm have dried out is best, if the soil is constantly wet it will prevent proper nutrient absorption and prevent enough oxygen getting to the roots too.
So, my suggestion would be to transplant her into a deeper pot, water only every 2-5 days and only once the top 2-3cm are dry and placing the seedling where it gets more light or stronger light. Remember to fill the new pot right up to the top, this way your plant will receive maximum light and it also provides much more room for roots to grow. More soil = more roots = more plant.
Good luck and happy growing!
Hope this helps,..........
Organoman.