I only nit-pick because I care. :-)

And of course it's always an option in later seasons if they need to do any cast reshuffles - wheel in a physicist as a consultant to the team.

Helen clearly watched a lot of Doctor Who as a child, and thus was mentally prepared for time travel from the outset. She probably went into science in order to make sure that when her moment came, she was eminently qualified to be an assistant to the Doctor who was respected in her own right.