How long have you had the fish for?
How long has the tank been set up for?
Have you added anything to the tank in the last 2 weeks?
It looks like Columnaris. This is a fast growing flesh eating bacteria that normally spreads across the mouth and face in a few days and the fish dies shortly after that.
It is uncommon in established tanks that haven't had anything new added to it, but is very common on newly imported fish. If you only got the fish in the last few days, it's probably Columnaris and will need antibiotics, which are hard to get in Australia.
You can add some salt in the mean time but you will need something stronger. If you have a spare tank, I would try to move her into it and then do a 90% water change and gravel clean on the main tank. This will reduce the chance of other fish catching it. Add salt to both tanks as well.
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SALT
You can add rock salt (often sold as aquarium salt), sea salt, or swimming pool salt to the aquarium at the dose rate of 2 heaped tablespoons of salt per 20 litres.
If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can add 2 heaped tablespoons per 20 litres and if there is no improvement after 48 hours, then increase it so there is a total of 4 heaped tablespoons of salt per 20 litres.
Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.
The salt will not affect the beneficial filter bacteria but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate (2 heaped tablespoons per 20 litres) will not affect fish, plants, shrimp or snails.
After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.
If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.
When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.
