She is fading away!
Clearly what has happened is that someone has gone back in time and done something to interfere with time and space — perhaps a teenage time traveller has somehow ended up as a member of Faithless instead of her — and now Sister Bliss is being 'removed from history' or something and now (subs please continue half-baked Back To The Future idea thanks)
Also, let's be honest, she looks absolutely ridiculous.
