I just read on rabbit.org (and want to confirm) that rabbits shed every 3 months and every second shedding is light followed three months later with a heavy shedding.
Gromit, I believe, is going through a very heavy shedding.  To the point that it looks like the outer coating (the harder bristles) are coming out and all is left is the soft down.  Does this make sense?  I'm watching her closely for any skin problems, going off her eating, etc.  But see nothing of the kind.  Just tons of hair coming out.