That appears to be either a bacterial or fungal infection IMO. Adding salt would be a good start, but may nuke your plants if you have live ones in there. (That will lead to other WQ issues). 2-3ppt is desirable. Best case scenario is that she is stressed, but the distinct ring around the head in the first pic leads me to believe otherwise.
How is the behavior/eating habits? How are the rest of the fish? Pics are small and grainy, but it looks pale, a little under weight, and hiding. My experience with them is that adults aren't very shy. All of the traits I just listed also lead me to believe you have a sick fish, and that it could spread to the rest of the tankmates.
Edit:
After seeing the 3rd pic containing 2 normally colored individuals, (which also look emaciated), I would second my guess that your female is sick with a skin infection.