If part of the tail actually became dried out and shrunken, then yes, it could very well be tail rotor,but dark color changes without any skin or scale changes are common for a number of reasons as well. So really the only way for us to tell is for you to post some photos of her tail, including some close ups of the area in question. Retained shed can cause infections because it can cut off the circulation to the rest of the tail, as well as bites and injuries.
Post a few photos of her and the tail and we'll be able to help...
