HMMM...I am not sure here but you did say you mixed 2 nutrient rich premium soils together and put a seedling in it?...are there any other additives such as perlite, vermiculite, dolomite anything to buffer the nutes at all? If no, ou have your answer. Roots are probably burnt to a crisp so no growth, and she needs help now! If yes to the additives, how much did you add and did you pre-flush the medium before planting. Does'nt really matter at this point. She needs a much more friendly environment if she is gonna survive. I would be likely to take some of ONE of those soils and, mix it 30% soil, 30% inert perlite, and 30% inert sphagnum or coco coir, vermiculite or really anything else that is stable and will keep the roots moist but aeratted. Put the soil in a large pot (I suggest a minimum 3 gallons so you can leave her there until harvest and avoid another transplant). Flush the soil with a good 3-5 gallons of ph'd water. Let it drain for several hours, at least 8. Then transplant her. She will NOT need more nutes for another 4 weeks or so. When feeding time comes, start at 1/4 dose and build up by 1/4 dose every 3rd feeding. Let the soil dry pretty darn good between waterings and feedings to allow oxygen to flow. I think this should clear her up. Good Luck!