I have never actually heard that before. I find it difficult to believe that any woman would do that to her own hair :) And when Charisma later appeared in a regular guest role on Charmed her hair was back to normal. This story wouldn't stem from Joss Whedon by any chance? He does have a tendency to rewrite history and blame his actors.

Any self-respecting woman would find it difficult to act with that on her head. I can't imagine standing front of a mirror with that thing on the top of my head, not even mentioning cameras ;)