I think it is a great story and you should contact The Daily Mail immediately. The more pressure to get this ridiculous situation sorted out, the better.
She can't have it both ways - if she elects to have the London relative's house as her principal residence, then that's the one that 'counts' for relief from CGT - even though she can't claim the relief as someone else owns it (the relative).
One suspects that she would find a way of wriggling from this, by having her film-buff husband as sole owner of the Redditch house.