Sadly, it's pretty obvious - you fed her to death. Cannabis generally does not need nor want nor can use any nutes for the first couple of weeks of their lives...
Start again, this one is unfortunately toast and there's no resurrection to be had. When the seedling pops up, keep the soil slightly moist, watering with only plain pH'd water around it... do not keep the soil wet all the time - it MUST have a wet/dry cycle and seedlings don't have the root system to handle more than a little moisture. Make sure you water out from the seedling so the roots, as they're forming, will go looking for water... if you water right up next to the stem, that can cause a damping off .... When, after a week or two, you introduce nutes, do so gradually - the first dose, if you're growing a photoperiod, should be about 1/2 strength but if you're growing an autoflower, it should be about 1/4 strength .... this is done to see if the plant is going to tolerate the nutes or not.... if it DOES tolerate them at that lower dosage, you can increase the strength the next time you feed. And always practice, once you get into feeding, a routine of water/feed/water/feed... some will even do water/water/feed/water/water/feed ....
Good luck with your next grow!