Jayedup.. I hope you still look at this post every now and then and sorry in advance if this doesn't reach you.
I had the same problem on my vanilla kush grow... And I can see from the young stalk that this was grown from seed? I had exactly the same problem...but I use coco. This is a clear case of stress...for this to be nitrogen would be very unlikely as your leaves aren't just yellowing they are getting brown,drying and dying. I suggest you follow what helped me out and re pot your plant... She will be fine and it's very easy mate. Get a towel and spread out to save mess.... Squeeze the sides of the pot tightly but not too tight so the medium compresses together and doesnt crumble off..Hold one hand on the stem firmly... And with the other hand tip the plant upside down. Place the plant normal way up and slowly shake and tap from the bottom to clear the root system as much as possible from the soil and make sure the bottom roots don't dangle too much because this will cause stress.... You can re plant in the same pot... But get some bat guano..preferably mexican with a nice nitrogen to pk level... Add in 20% perlite from your local garden shop and mix that baby up.... Make a hole half way down and simply place your baby right back in then lightly pat down and cover.... This will bring her back to life pretty much immediately... I hope that helps!