Your tanks overstocked if you sig stocking still the same.
What are your water stats in ammonia, nitrite, nitrate, and ph.
Could she of hurt her mouth on anything sharp in the tank.
Is the mouth also swollen.
Any white strands, cotton wool, or bleaching of the mouth area.
Is the mouth rotting away.
is she able to close her mouth. Meaning is the mouth always open.
Any redness on the belly region.
Does your heater have a heater guard.
If you have gravel in the tank is it sharp or have sharp edges.
Hows the fish breathing.