I'd think I have to join Glee. Or at least watch it, for once. XD
How would you react if you were Sir Arthur Conan Doyle's long lost great great great grandchild?
If he tells her personally then that would be (I think) the best (and most romantic) way... however the Ran seeing Conan transform to Shinichi idea is not that bad. If it were to happen that way, it'd be thrilling to watch it happen!