Tropical Fish Ailments - Mollies?

My female molly - pearl white - has developed a growth on top and just behind the head, immediately in front of the fin. It has pinky colouration and looks a little like a crew cut. In addition there is what looks like a bruise on top of the head between the eyes. Her movements are slow and give the appearance of rocking backward and forward. She is eating ok but otherwise doesn't look too bright. This seems to have only happened in the last 2 or 3 days. Any suggestions? Would it be best to euthenase?