Sounds like popeye, along with the redness indicates a bacterial infection. From the info in your sig it appears that the molly is in its own tank, which will make medicating much easier. Most any lfs carries Maracyn and MaracynII, these can be used together for gram positive and gram negative bacteria.
When using antibiotics such as these I suggest changing 50% of the water daily, as fresh water is one of the best preventave medicines for fish.