I know, but what was she like when she had her own TARDIS? Who would be have as her companions in an adventure through time and space? What if she'd never left that life behind? Is she a friend or foe of the Doctor's?
As I said, this is a chance to just have fun with some weird and wonderful combinations.
I have started an entry, where Delenn from Babylon 5 is one of Guinan's companions...