I've heard of rosehairs fasting for years at a time. Don't let it worry you. As long as your rosie has a full water dish, and a full looking abdomen that does not look shriveled or wrinkled, it is fine. One of the most telling signs for me with a rosie that it is going to moult is that the mirror patch on the abdomen starts looking like a peeling scab.

Even after yours looks like that it could still be months before anything happens, rosies do everything slowly. I personally love them, but they are the champions at the waiting game.