Did she talk to them about it? This sounds serious! There is a chance that medicine might do this, but I would think that it would be extremely rare to happen. She needs to go back and find out what it is for sure, you don't want to take chances with it. Is there also a chance that this might be bruising? I hope so. Hope this helps, good luck.
Advice is to see your Doctor..Could be many causes, such as Heart, Liver problems..Circulatory problems cause this.
I am in agreement with the 2 answers above. This could be a circulation problem or the aftermath of a circulation issue. It could be from swelling in the legs that has subsided. It could be from medication, whatever it is, I believe it to be serious enough to warrant a thorough inspection by a Dr.