Yes fungus. Mollies seem to be prone to it. Do you have other fish in the tank? You really need to remove the molly or it will spread. If you do not have a tank you can use a small storage bin as a temp quarantine tank. It will require lots of water changes though. Always good to keep some type of water tight container to QT, an extra filter, and heater. A large glass jar can work in a pinch. Get some type of fungus medicine and treat according to directions. Add some Kosher or pickling salt to the tank. Use about a teaspoon per 10 gallons of water. I have done this with mystery snails and shrimp in the tank and had no problems. Salt is always my go to first. You can use up to a tablespoon per 10 gallons if you have to. Just do water changes between adding salt doses. It builds up in the tank if you don't.