If that's an injury, it's not the pearls you should be blaming (the paradisefish are more likely and they often do this kind of thing overnight).
On the upside, if it's an injury, a clean, CYCLED hospital tank would be enough to ward off secondary infections. Also, BTW, it's not so much fungal infections you need to worry about (these only ever attack already dead tissue) but secondary bacterial ones like those responsible for finrot (columnaris/aeromonas). Excessively high temperatures make fish particularly susceptible to these and clean water is essential.
The meds. mentioned above still work though
edit: BTW, your catfish won't like the treatment but if you don't have a cycled tank, there's no point isolating the gourami as she'll die of ammonia poisoning. Instead, you can just skip the meds. and focus on clean water and slightly lowering the temp. (very gardualy though) to prevent infections.
Oh and, to be on the safe side, did these appear overnight or have they been developing over a longer time period? If these are ulcers, you may not be able to do anything except euthanise once she stops eating.
