It's hard to diagnose her if you can't really see anything too abnormal. You do know that she is hiding (could be from illness, bullying or stress), swimming/resting at a slant (constipation or illness) and not eating. It will be telling when she gets put in HT cuz if her behavior normalizes then she was probably being bullied/stressed. Keep fasting on the shorter side with juvenile fish like 1-2 days, or instead, you can feed foods lightly that don't constipate like veggies (peas) or chopped frozen bloodworms. Stay away from dried foods even if soaked since they can still be difficult to digest. I don't find that omnivores get constipation very often so if she gets moved to HT and still acts sick, I would treat her with M2 (or Kana in the water) and RI+ (or Maracide) to cover for bacterial and parasitic infections. Fertilizers aren't the likely culprit here.

Let us know how she does,

Barb