Not one I can help on I'm afraid ... I don't really have any interest in 'theatre organs' and consequently, other than hearing of Carolyn Riddick, I know nothing about her or her career. A great many theatre organists at some point in their career 'crossover' into the world of electronic organs even if only briefly ... but I have heard nothing of Carolyn doing that either.
Presumably you have checked with 'Organfax' ... they do tend to have details of most active organists in the UK
Best regards
Mike