Columnaris (aka mouth fungus) is a nasty flesh eating bacteria that normally kills infected fish within a couple of days of showing symptoms. The most common symptom is a white mouth, which rapidly spreads over the face and head. The fish are usually dead within 24-48 hours of showing the white mouth.
Fish can also get a flesh eating bacterial infection on their body and this spreads through the muscle tissue and kills the fish within a couple of days. This type of infection is uncommon on mollies but the mouth infection can occur on them, especially if they are newly imported from Asia.
To treat true Columnaris infections, you need anti-biotics.
The molly in question does not in my opinion have Columnaris.